org.apache.hadoop.conf.Configuration.java Source code

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/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.conf;

import com.ctc.wstx.api.ReaderConfig;
import com.ctc.wstx.io.StreamBootstrapper;
import com.ctc.wstx.io.SystemId;
import com.ctc.wstx.stax.WstxInputFactory;
import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonGenerator;
import com.google.common.annotations.VisibleForTesting;

import java.io.BufferedInputStream;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Reader;
import java.io.Writer;
import java.lang.ref.WeakReference;
import java.net.InetSocketAddress;
import java.net.JarURLConnection;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Properties;
import java.util.Set;
import java.util.StringTokenizer;
import java.util.WeakHashMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;

import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamReader;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import com.google.common.base.Charsets;
import org.apache.commons.collections.map.UnmodifiableMap;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.fs.CommonConfigurationKeysPublic;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.fs.CommonConfigurationKeys;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableUtils;
import org.apache.hadoop.net.NetUtils;
import org.apache.hadoop.security.UserGroupInformation;
import org.apache.hadoop.security.alias.CredentialProvider;
import org.apache.hadoop.security.alias.CredentialProvider.CredentialEntry;
import org.apache.hadoop.security.alias.CredentialProviderFactory;
import org.apache.hadoop.util.ReflectionUtils;
import org.apache.hadoop.util.StringInterner;
import org.apache.hadoop.util.StringUtils;
import org.codehaus.stax2.XMLStreamReader2;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;

import com.google.common.base.Preconditions;
import com.google.common.base.Strings;

import static org.apache.commons.lang3.StringUtils.isBlank;
import static org.apache.commons.lang3.StringUtils.isNotBlank;

/**
 * Provides access to configuration parameters.
 *
 * <h4 id="Resources">Resources</h4>
 *
 * <p>Configurations are specified by resources. A resource contains a set of
 * name/value pairs as XML data. Each resource is named by either a 
 * <code>String</code> or by a {@link Path}. If named by a <code>String</code>, 
 * then the classpath is examined for a file with that name.  If named by a 
 * <code>Path</code>, then the local filesystem is examined directly, without 
 * referring to the classpath.
 *
 * <p>Unless explicitly turned off, Hadoop by default specifies two 
 * resources, loaded in-order from the classpath: <ol>
 * <li><tt>
 * <a href="{@docRoot}/../hadoop-project-dist/hadoop-common/core-default.xml">
 * core-default.xml</a></tt>: Read-only defaults for hadoop.</li>
 * <li><tt>core-site.xml</tt>: Site-specific configuration for a given hadoop
 * installation.</li>
 * </ol>
 * Applications may add additional resources, which are loaded
 * subsequent to these resources in the order they are added.
 * 
 * <h4 id="FinalParams">Final Parameters</h4>
 *
 * <p>Configuration parameters may be declared <i>final</i>. 
 * Once a resource declares a value final, no subsequently-loaded 
 * resource can alter that value.  
 * For example, one might define a final parameter with:
 * <tt><pre>
 *  &lt;property&gt;
 *    &lt;name&gt;dfs.hosts.include&lt;/name&gt;
 *    &lt;value&gt;/etc/hadoop/conf/hosts.include&lt;/value&gt;
 *    <b>&lt;final&gt;true&lt;/final&gt;</b>
 *  &lt;/property&gt;</pre></tt>
 *
 * Administrators typically define parameters as final in 
 * <tt>core-site.xml</tt> for values that user applications may not alter.
 *
 * <h4 id="VariableExpansion">Variable Expansion</h4>
 *
 * <p>Value strings are first processed for <i>variable expansion</i>. The
 * available properties are:<ol>
 * <li>Other properties defined in this Configuration; and, if a name is
 * undefined here,</li>
 * <li>Environment variables in {@link System#getenv()} if a name starts with
 * "env.", or</li>
 * <li>Properties in {@link System#getProperties()}.</li>
 * </ol>
 *
 * <p>For example, if a configuration resource contains the following property
 * definitions: 
 * <tt><pre>
 *  &lt;property&gt;
 *    &lt;name&gt;basedir&lt;/name&gt;
 *    &lt;value&gt;/user/${<i>user.name</i>}&lt;/value&gt;
 *  &lt;/property&gt;
 *  
 *  &lt;property&gt;
 *    &lt;name&gt;tempdir&lt;/name&gt;
 *    &lt;value&gt;${<i>basedir</i>}/tmp&lt;/value&gt;
 *  &lt;/property&gt;
 *
 *  &lt;property&gt;
 *    &lt;name&gt;otherdir&lt;/name&gt;
 *    &lt;value&gt;${<i>env.BASE_DIR</i>}/other&lt;/value&gt;
 *  &lt;/property&gt;
 *  </pre></tt>
 *
 * <p>When <tt>conf.get("tempdir")</tt> is called, then <tt>${<i>basedir</i>}</tt>
 * will be resolved to another property in this Configuration, while
 * <tt>${<i>user.name</i>}</tt> would then ordinarily be resolved to the value
 * of the System property with that name.
 * <p>When <tt>conf.get("otherdir")</tt> is called, then <tt>${<i>env.BASE_DIR</i>}</tt>
 * will be resolved to the value of the <tt>${<i>BASE_DIR</i>}</tt> environment variable.
 * It supports <tt>${<i>env.NAME:-default</i>}</tt> and <tt>${<i>env.NAME-default</i>}</tt> notations.
 * The former is resolved to "default" if <tt>${<i>NAME</i>}</tt> environment variable is undefined
 * or its value is empty.
 * The latter behaves the same way only if <tt>${<i>NAME</i>}</tt> is undefined.
 * <p>By default, warnings will be given to any deprecated configuration 
 * parameters and these are suppressible by configuring
 * <tt>log4j.logger.org.apache.hadoop.conf.Configuration.deprecation</tt> in
 * log4j.properties file.
 *
 * <h4 id="Tags">Tags</h4>
 *
 * <p>Optionally we can tag related properties together by using tag
 * attributes. System tags are defined by hadoop.tags.system property. Users
 * can define there own custom tags in  hadoop.tags.custom property.
 *
 * <p>For example, we can tag existing property as:
 * <tt><pre>
 *  &lt;property&gt;
 *    &lt;name&gt;dfs.replication&lt;/name&gt;
 *    &lt;value&gt;3&lt;/value&gt;
 *    &lt;tag&gt;HDFS,REQUIRED&lt;/tag&gt;
 *  &lt;/property&gt;
 *
 *  &lt;property&gt;
 *    &lt;name&gt;dfs.data.transfer.protection&lt;/name&gt;
 *    &lt;value&gt;3&lt;/value&gt;
 *    &lt;tag&gt;HDFS,SECURITY&lt;/tag&gt;
 *  &lt;/property&gt;
 * </pre></tt>
 * <p> Properties marked with tags can be retrieved with <tt>conf
 * .getAllPropertiesByTag("HDFS")</tt> or <tt>conf.getAllPropertiesByTags
 * (Arrays.asList("YARN","SECURITY"))</tt>.</p>
 */
@InterfaceAudience.Public
@InterfaceStability.Stable
public class Configuration implements Iterable<Map.Entry<String, String>>, Writable {
    private static final Logger LOG = LoggerFactory.getLogger(Configuration.class);

    private static final Logger LOG_DEPRECATION = LoggerFactory
            .getLogger("org.apache.hadoop.conf.Configuration.deprecation");
    private static final Set<String> TAGS = ConcurrentHashMap.newKeySet();

    private boolean quietmode = true;

    private static final String DEFAULT_STRING_CHECK = "testingforemptydefaultvalue";

    private static boolean restrictSystemPropsDefault = false;
    private boolean restrictSystemProps = restrictSystemPropsDefault;
    private boolean allowNullValueProperties = false;

    private static class Resource {
        private final Object resource;
        private final String name;
        private final boolean restrictParser;

        public Resource(Object resource) {
            this(resource, resource.toString());
        }

        public Resource(Object resource, boolean useRestrictedParser) {
            this(resource, resource.toString(), useRestrictedParser);
        }

        public Resource(Object resource, String name) {
            this(resource, name, getRestrictParserDefault(resource));
        }

        public Resource(Object resource, String name, boolean restrictParser) {
            this.resource = resource;
            this.name = name;
            this.restrictParser = restrictParser;
        }

        public String getName() {
            return name;
        }

        public Object getResource() {
            return resource;
        }

        public boolean isParserRestricted() {
            return restrictParser;
        }

        @Override
        public String toString() {
            return name;
        }

        private static boolean getRestrictParserDefault(Object resource) {
            if (resource instanceof String || !UserGroupInformation.isInitialized()) {
                return false;
            }
            UserGroupInformation user;
            try {
                user = UserGroupInformation.getCurrentUser();
            } catch (IOException e) {
                throw new RuntimeException("Unable to determine current user", e);
            }
            return user.getRealUser() != null;
        }
    }

    /**
     * List of configuration resources.
     */
    private ArrayList<Resource> resources = new ArrayList<Resource>();

    /**
     * The value reported as the setting resource when a key is set
     * by code rather than a file resource by dumpConfiguration.
     */
    static final String UNKNOWN_RESOURCE = "Unknown";

    /**
     * List of configuration parameters marked <b>final</b>. 
     */
    private Set<String> finalParameters = Collections.newSetFromMap(new ConcurrentHashMap<String, Boolean>());

    private boolean loadDefaults = true;

    /**
     * Configuration objects
     */
    private static final WeakHashMap<Configuration, Object> REGISTRY = new WeakHashMap<Configuration, Object>();

    /**
     * Map to hold properties by there tag groupings.
     */
    private final Map<String, Properties> propertyTagsMap = new ConcurrentHashMap<>();

    /**
     * List of default Resources. Resources are loaded in the order of the list 
     * entries
     */
    private static final CopyOnWriteArrayList<String> defaultResources = new CopyOnWriteArrayList<String>();

    private static final Map<ClassLoader, Map<String, WeakReference<Class<?>>>> CACHE_CLASSES = new WeakHashMap<ClassLoader, Map<String, WeakReference<Class<?>>>>();

    /**
     * Sentinel value to store negative cache results in {@link #CACHE_CLASSES}.
     */
    private static final Class<?> NEGATIVE_CACHE_SENTINEL = NegativeCacheSentinel.class;

    /**
     * Stores the mapping of key to the resource which modifies or loads 
     * the key most recently. Created lazily to avoid wasting memory.
     */
    private volatile Map<String, String[]> updatingResource;

    /**
     * Specify exact input factory to avoid time finding correct one.
     * Factory is reusable across un-synchronized threads once initialized
     */
    private static final WstxInputFactory XML_INPUT_FACTORY = new WstxInputFactory();

    /**
     * Class to keep the information about the keys which replace the deprecated
     * ones.
     * 
     * This class stores the new keys which replace the deprecated keys and also
     * gives a provision to have a custom message for each of the deprecated key
     * that is being replaced. It also provides method to get the appropriate
     * warning message which can be logged whenever the deprecated key is used.
     */
    private static class DeprecatedKeyInfo {
        private final String[] newKeys;
        private final String customMessage;
        private final AtomicBoolean accessed = new AtomicBoolean(false);

        DeprecatedKeyInfo(String[] newKeys, String customMessage) {
            this.newKeys = newKeys;
            this.customMessage = customMessage;
        }

        private final String getWarningMessage(String key) {
            return getWarningMessage(key, null);
        }

        /**
         * Method to provide the warning message. It gives the custom message if
         * non-null, and default message otherwise.
         * @param key the associated deprecated key.
         * @param source the property source.
         * @return message that is to be logged when a deprecated key is used.
         */
        private String getWarningMessage(String key, String source) {
            String warningMessage;
            if (customMessage == null) {
                StringBuilder message = new StringBuilder(key);
                if (source != null) {
                    message.append(" in " + source);
                }
                message.append(" is deprecated. Instead, use ");
                for (int i = 0; i < newKeys.length; i++) {
                    message.append(newKeys[i]);
                    if (i != newKeys.length - 1) {
                        message.append(", ");
                    }
                }
                warningMessage = message.toString();
            } else {
                warningMessage = customMessage;
            }
            return warningMessage;
        }

        boolean getAndSetAccessed() {
            return accessed.getAndSet(true);
        }

        public void clearAccessed() {
            accessed.set(false);
        }
    }

    /**
     * A pending addition to the global set of deprecated keys.
     */
    public static class DeprecationDelta {
        private final String key;
        private final String[] newKeys;
        private final String customMessage;

        DeprecationDelta(String key, String[] newKeys, String customMessage) {
            Preconditions.checkNotNull(key);
            Preconditions.checkNotNull(newKeys);
            Preconditions.checkArgument(newKeys.length > 0);
            this.key = key;
            this.newKeys = newKeys;
            this.customMessage = customMessage;
        }

        public DeprecationDelta(String key, String newKey, String customMessage) {
            this(key, new String[] { newKey }, customMessage);
        }

        public DeprecationDelta(String key, String newKey) {
            this(key, new String[] { newKey }, null);
        }

        public String getKey() {
            return key;
        }

        public String[] getNewKeys() {
            return newKeys;
        }

        public String getCustomMessage() {
            return customMessage;
        }
    }

    /**
     * The set of all keys which are deprecated.
     *
     * DeprecationContext objects are immutable.
     */
    private static class DeprecationContext {
        /**
         * Stores the deprecated keys, the new keys which replace the deprecated keys
         * and custom message(if any provided).
         */
        private final Map<String, DeprecatedKeyInfo> deprecatedKeyMap;

        /**
         * Stores a mapping from superseding keys to the keys which they deprecate.
         */
        private final Map<String, String> reverseDeprecatedKeyMap;

        /**
         * Create a new DeprecationContext by copying a previous DeprecationContext
         * and adding some deltas.
         *
         * @param other   The previous deprecation context to copy, or null to start
         *                from nothing.
         * @param deltas  The deltas to apply.
         */
        @SuppressWarnings("unchecked")
        DeprecationContext(DeprecationContext other, DeprecationDelta[] deltas) {
            HashMap<String, DeprecatedKeyInfo> newDeprecatedKeyMap = new HashMap<String, DeprecatedKeyInfo>();
            HashMap<String, String> newReverseDeprecatedKeyMap = new HashMap<String, String>();
            if (other != null) {
                for (Entry<String, DeprecatedKeyInfo> entry : other.deprecatedKeyMap.entrySet()) {
                    newDeprecatedKeyMap.put(entry.getKey(), entry.getValue());
                }
                for (Entry<String, String> entry : other.reverseDeprecatedKeyMap.entrySet()) {
                    newReverseDeprecatedKeyMap.put(entry.getKey(), entry.getValue());
                }
            }
            for (DeprecationDelta delta : deltas) {
                if (!newDeprecatedKeyMap.containsKey(delta.getKey())) {
                    DeprecatedKeyInfo newKeyInfo = new DeprecatedKeyInfo(delta.getNewKeys(),
                            delta.getCustomMessage());
                    newDeprecatedKeyMap.put(delta.key, newKeyInfo);
                    for (String newKey : delta.getNewKeys()) {
                        newReverseDeprecatedKeyMap.put(newKey, delta.key);
                    }
                }
            }
            this.deprecatedKeyMap = UnmodifiableMap.decorate(newDeprecatedKeyMap);
            this.reverseDeprecatedKeyMap = UnmodifiableMap.decorate(newReverseDeprecatedKeyMap);
        }

        Map<String, DeprecatedKeyInfo> getDeprecatedKeyMap() {
            return deprecatedKeyMap;
        }

        Map<String, String> getReverseDeprecatedKeyMap() {
            return reverseDeprecatedKeyMap;
        }
    }

    private static DeprecationDelta[] defaultDeprecations = new DeprecationDelta[] {
            new DeprecationDelta("topology.script.file.name",
                    CommonConfigurationKeys.NET_TOPOLOGY_SCRIPT_FILE_NAME_KEY),
            new DeprecationDelta("topology.script.number.args",
                    CommonConfigurationKeys.NET_TOPOLOGY_SCRIPT_NUMBER_ARGS_KEY),
            new DeprecationDelta("hadoop.configured.node.mapping",
                    CommonConfigurationKeys.NET_TOPOLOGY_CONFIGURED_NODE_MAPPING_KEY),
            new DeprecationDelta("topology.node.switch.mapping.impl",
                    CommonConfigurationKeys.NET_TOPOLOGY_NODE_SWITCH_MAPPING_IMPL_KEY),
            new DeprecationDelta("dfs.df.interval", CommonConfigurationKeys.FS_DF_INTERVAL_KEY),
            new DeprecationDelta("fs.default.name", CommonConfigurationKeys.FS_DEFAULT_NAME_KEY),
            new DeprecationDelta("dfs.umaskmode", CommonConfigurationKeys.FS_PERMISSIONS_UMASK_KEY),
            new DeprecationDelta("dfs.nfs.exports.allowed.hosts",
                    CommonConfigurationKeys.NFS_EXPORTS_ALLOWED_HOSTS_KEY) };

    /**
     * The global DeprecationContext.
     */
    private static AtomicReference<DeprecationContext> deprecationContext = new AtomicReference<DeprecationContext>(
            new DeprecationContext(null, defaultDeprecations));

    /**
     * Adds a set of deprecated keys to the global deprecations.
     *
     * This method is lockless.  It works by means of creating a new
     * DeprecationContext based on the old one, and then atomically swapping in
     * the new context.  If someone else updated the context in between us reading
     * the old context and swapping in the new one, we try again until we win the
     * race.
     *
     * @param deltas   The deprecations to add.
     */
    public static void addDeprecations(DeprecationDelta[] deltas) {
        DeprecationContext prev, next;
        do {
            prev = deprecationContext.get();
            next = new DeprecationContext(prev, deltas);
        } while (!deprecationContext.compareAndSet(prev, next));
    }

    /**
     * Adds the deprecated key to the global deprecation map.
     * It does not override any existing entries in the deprecation map.
     * This is to be used only by the developers in order to add deprecation of
     * keys, and attempts to call this method after loading resources once,
     * would lead to <tt>UnsupportedOperationException</tt>
     * 
     * If a key is deprecated in favor of multiple keys, they are all treated as 
     * aliases of each other, and setting any one of them resets all the others 
     * to the new value.
     *
     * If you have multiple deprecation entries to add, it is more efficient to
     * use #addDeprecations(DeprecationDelta[] deltas) instead.
     * 
     * @param key
     * @param newKeys
     * @param customMessage
     * @deprecated use {@link #addDeprecation(String key, String newKey,
        String customMessage)} instead
     */
    @Deprecated
    public static void addDeprecation(String key, String[] newKeys, String customMessage) {
        addDeprecations(new DeprecationDelta[] { new DeprecationDelta(key, newKeys, customMessage) });
    }

    /**
     * Adds the deprecated key to the global deprecation map.
     * It does not override any existing entries in the deprecation map.
     * This is to be used only by the developers in order to add deprecation of
     * keys, and attempts to call this method after loading resources once,
     * would lead to <tt>UnsupportedOperationException</tt>
     * 
     * If you have multiple deprecation entries to add, it is more efficient to
     * use #addDeprecations(DeprecationDelta[] deltas) instead.
     *
     * @param key
     * @param newKey
     * @param customMessage
     */
    public static void addDeprecation(String key, String newKey, String customMessage) {
        addDeprecation(key, new String[] { newKey }, customMessage);
    }

    /**
     * Adds the deprecated key to the global deprecation map when no custom
     * message is provided.
     * It does not override any existing entries in the deprecation map.
     * This is to be used only by the developers in order to add deprecation of
     * keys, and attempts to call this method after loading resources once,
     * would lead to <tt>UnsupportedOperationException</tt>
     * 
     * If a key is deprecated in favor of multiple keys, they are all treated as 
     * aliases of each other, and setting any one of them resets all the others 
     * to the new value.
     * 
     * If you have multiple deprecation entries to add, it is more efficient to
     * use #addDeprecations(DeprecationDelta[] deltas) instead.
     *
     * @param key Key that is to be deprecated
     * @param newKeys list of keys that take up the values of deprecated key
     * @deprecated use {@link #addDeprecation(String key, String newKey)} instead
     */
    @Deprecated
    public static void addDeprecation(String key, String[] newKeys) {
        addDeprecation(key, newKeys, null);
    }

    /**
     * Adds the deprecated key to the global deprecation map when no custom
     * message is provided.
     * It does not override any existing entries in the deprecation map.
     * This is to be used only by the developers in order to add deprecation of
     * keys, and attempts to call this method after loading resources once,
     * would lead to <tt>UnsupportedOperationException</tt>
     * 
     * If you have multiple deprecation entries to add, it is more efficient to
     * use #addDeprecations(DeprecationDelta[] deltas) instead.
     *
     * @param key Key that is to be deprecated
     * @param newKey key that takes up the value of deprecated key
     */
    public static void addDeprecation(String key, String newKey) {
        addDeprecation(key, new String[] { newKey }, null);
    }

    /**
     * checks whether the given <code>key</code> is deprecated.
     * 
     * @param key the parameter which is to be checked for deprecation
     * @return <code>true</code> if the key is deprecated and 
     *         <code>false</code> otherwise.
     */
    public static boolean isDeprecated(String key) {
        return deprecationContext.get().getDeprecatedKeyMap().containsKey(key);
    }

    private static String getDeprecatedKey(String key) {
        return deprecationContext.get().getReverseDeprecatedKeyMap().get(key);
    }

    private static DeprecatedKeyInfo getDeprecatedKeyInfo(String key) {
        return deprecationContext.get().getDeprecatedKeyMap().get(key);
    }

    /**
     * Sets all deprecated properties that are not currently set but have a
     * corresponding new property that is set. Useful for iterating the
     * properties when all deprecated properties for currently set properties
     * need to be present.
     */
    public void setDeprecatedProperties() {
        DeprecationContext deprecations = deprecationContext.get();
        Properties props = getProps();
        Properties overlay = getOverlay();
        for (Map.Entry<String, DeprecatedKeyInfo> entry : deprecations.getDeprecatedKeyMap().entrySet()) {
            String depKey = entry.getKey();
            if (!overlay.contains(depKey)) {
                for (String newKey : entry.getValue().newKeys) {
                    String val = overlay.getProperty(newKey);
                    if (val != null) {
                        props.setProperty(depKey, val);
                        overlay.setProperty(depKey, val);
                        break;
                    }
                }
            }
        }
    }

    /**
     * Checks for the presence of the property <code>name</code> in the
     * deprecation map. Returns the first of the list of new keys if present
     * in the deprecation map or the <code>name</code> itself. If the property
     * is not presently set but the property map contains an entry for the
     * deprecated key, the value of the deprecated key is set as the value for
     * the provided property name.
     *
     * @param deprecations deprecation context
     * @param name the property name
     * @return the first property in the list of properties mapping
     *         the <code>name</code> or the <code>name</code> itself.
     */
    private String[] handleDeprecation(DeprecationContext deprecations, String name) {
        if (null != name) {
            name = name.trim();
        }
        // Initialize the return value with requested name
        String[] names = new String[] { name };
        // Deprecated keys are logged once and an updated names are returned
        DeprecatedKeyInfo keyInfo = deprecations.getDeprecatedKeyMap().get(name);
        if (keyInfo != null) {
            if (!keyInfo.getAndSetAccessed()) {
                logDeprecation(keyInfo.getWarningMessage(name));
            }
            // Override return value for deprecated keys
            names = keyInfo.newKeys;
        }
        // If there are no overlay values we can return early
        Properties overlayProperties = getOverlay();
        if (overlayProperties.isEmpty()) {
            return names;
        }
        // Update properties and overlays with reverse lookup values
        for (String n : names) {
            String deprecatedKey = deprecations.getReverseDeprecatedKeyMap().get(n);
            if (deprecatedKey != null && !overlayProperties.containsKey(n)) {
                String deprecatedValue = overlayProperties.getProperty(deprecatedKey);
                if (deprecatedValue != null) {
                    getProps().setProperty(n, deprecatedValue);
                    overlayProperties.setProperty(n, deprecatedValue);
                }
            }
        }
        return names;
    }

    private void handleDeprecation() {
        LOG.debug("Handling deprecation for all properties in config...");
        DeprecationContext deprecations = deprecationContext.get();
        Set<Object> keys = new HashSet<Object>();
        keys.addAll(getProps().keySet());
        for (Object item : keys) {
            LOG.debug("Handling deprecation for " + (String) item);
            handleDeprecation(deprecations, (String) item);
        }
    }

    static {
        // Add default resources
        addDefaultResource("core-default.xml");
        addDefaultResource("core-site.xml");

        // print deprecation warning if hadoop-site.xml is found in classpath
        ClassLoader cL = Thread.currentThread().getContextClassLoader();
        if (cL == null) {
            cL = Configuration.class.getClassLoader();
        }
        if (cL.getResource("hadoop-site.xml") != null) {
            LOG.warn("DEPRECATED: hadoop-site.xml found in the classpath. "
                    + "Usage of hadoop-site.xml is deprecated. Instead use core-site.xml, "
                    + "mapred-site.xml and hdfs-site.xml to override properties of "
                    + "core-default.xml, mapred-default.xml and hdfs-default.xml " + "respectively");
            addDefaultResource("hadoop-site.xml");
        }
    }

    private Properties properties;
    private Properties overlay;
    private ClassLoader classLoader;
    {
        classLoader = Thread.currentThread().getContextClassLoader();
        if (classLoader == null) {
            classLoader = Configuration.class.getClassLoader();
        }
    }

    /** A new configuration. */
    public Configuration() {
        this(true);
    }

    /** A new configuration where the behavior of reading from the default 
     * resources can be turned off.
     * 
     * If the parameter {@code loadDefaults} is false, the new instance
     * will not load resources from the default files. 
     * @param loadDefaults specifies whether to load from the default files
     */
    public Configuration(boolean loadDefaults) {
        this.loadDefaults = loadDefaults;

        synchronized (Configuration.class) {
            REGISTRY.put(this, null);
        }
    }

    /** 
     * A new configuration with the same settings cloned from another.
     * 
     * @param other the configuration from which to clone settings.
     */
    @SuppressWarnings("unchecked")
    public Configuration(Configuration other) {
        synchronized (other) {
            // Make sure we clone a finalized state
            // Resources like input streams can be processed only once
            other.getProps();
            this.resources = (ArrayList<Resource>) other.resources.clone();
            if (other.properties != null) {
                this.properties = (Properties) other.properties.clone();
            }

            if (other.overlay != null) {
                this.overlay = (Properties) other.overlay.clone();
            }

            this.restrictSystemProps = other.restrictSystemProps;
            if (other.updatingResource != null) {
                this.updatingResource = new ConcurrentHashMap<String, String[]>(other.updatingResource);
            }
            this.finalParameters = Collections.newSetFromMap(new ConcurrentHashMap<String, Boolean>());
            this.finalParameters.addAll(other.finalParameters);
            this.propertyTagsMap.putAll(other.propertyTagsMap);
        }

        synchronized (Configuration.class) {
            REGISTRY.put(this, null);
        }
        this.classLoader = other.classLoader;
        this.loadDefaults = other.loadDefaults;
        setQuietMode(other.getQuietMode());
    }

    /**
     * Reload existing configuration instances.
     */
    public static synchronized void reloadExistingConfigurations() {
        if (LOG.isDebugEnabled()) {
            LOG.debug("Reloading " + REGISTRY.keySet().size() + " existing configurations");
        }
        for (Configuration conf : REGISTRY.keySet()) {
            conf.reloadConfiguration();
        }
    }

    /**
     * Add a default resource. Resources are loaded in the order of the resources 
     * added.
     * @param name file name. File should be present in the classpath.
     */
    public static synchronized void addDefaultResource(String name) {
        if (!defaultResources.contains(name)) {
            defaultResources.add(name);
            for (Configuration conf : REGISTRY.keySet()) {
                if (conf.loadDefaults) {
                    conf.reloadConfiguration();
                }
            }
        }
    }

    public static void setRestrictSystemPropertiesDefault(boolean val) {
        restrictSystemPropsDefault = val;
    }

    public void setRestrictSystemProperties(boolean val) {
        this.restrictSystemProps = val;
    }

    /**
     * Add a configuration resource. 
     * 
     * The properties of this resource will override properties of previously 
     * added resources, unless they were marked <a href="#Final">final</a>. 
     * 
     * @param name resource to be added, the classpath is examined for a file 
     *             with that name.
     */
    public void addResource(String name) {
        addResourceObject(new Resource(name));
    }

    public void addResource(String name, boolean restrictedParser) {
        addResourceObject(new Resource(name, restrictedParser));
    }

    /**
     * Add a configuration resource. 
     * 
     * The properties of this resource will override properties of previously 
     * added resources, unless they were marked <a href="#Final">final</a>. 
     * 
     * @param url url of the resource to be added, the local filesystem is 
     *            examined directly to find the resource, without referring to 
     *            the classpath.
     */
    public void addResource(URL url) {
        addResourceObject(new Resource(url));
    }

    public void addResource(URL url, boolean restrictedParser) {
        addResourceObject(new Resource(url, restrictedParser));
    }

    /**
     * Add a configuration resource. 
     * 
     * The properties of this resource will override properties of previously 
     * added resources, unless they were marked <a href="#Final">final</a>. 
     * 
     * @param file file-path of resource to be added, the local filesystem is
     *             examined directly to find the resource, without referring to 
     *             the classpath.
     */
    public void addResource(Path file) {
        addResourceObject(new Resource(file));
    }

    public void addResource(Path file, boolean restrictedParser) {
        addResourceObject(new Resource(file, restrictedParser));
    }

    /**
     * Add a configuration resource. 
     * 
     * The properties of this resource will override properties of previously 
     * added resources, unless they were marked <a href="#Final">final</a>. 
     * 
     * WARNING: The contents of the InputStream will be cached, by this method. 
     * So use this sparingly because it does increase the memory consumption.
     * 
     * @param in InputStream to deserialize the object from. In will be read from
     * when a get or set is called next.  After it is read the stream will be
     * closed. 
     */
    public void addResource(InputStream in) {
        addResourceObject(new Resource(in));
    }

    public void addResource(InputStream in, boolean restrictedParser) {
        addResourceObject(new Resource(in, restrictedParser));
    }

    /**
     * Add a configuration resource. 
     * 
     * The properties of this resource will override properties of previously 
     * added resources, unless they were marked <a href="#Final">final</a>. 
     * 
     * @param in InputStream to deserialize the object from.
     * @param name the name of the resource because InputStream.toString is not
     * very descriptive some times.  
     */
    public void addResource(InputStream in, String name) {
        addResourceObject(new Resource(in, name));
    }

    public void addResource(InputStream in, String name, boolean restrictedParser) {
        addResourceObject(new Resource(in, name, restrictedParser));
    }

    /**
     * Add a configuration resource.
     *
     * The properties of this resource will override properties of previously
     * added resources, unless they were marked <a href="#Final">final</a>.
     *
     * @param conf Configuration object from which to load properties
     */
    public void addResource(Configuration conf) {
        addResourceObject(new Resource(conf.getProps(), conf.restrictSystemProps));
    }

    /**
     * Reload configuration from previously added resources.
     *
     * This method will clear all the configuration read from the added 
     * resources, and final parameters. This will make the resources to 
     * be read again before accessing the values. Values that are added
     * via set methods will overlay values read from the resources.
     */
    public synchronized void reloadConfiguration() {
        properties = null; // trigger reload
        finalParameters.clear(); // clear site-limits
    }

    private synchronized void addResourceObject(Resource resource) {
        resources.add(resource); // add to resources
        restrictSystemProps |= resource.isParserRestricted();
        reloadConfiguration();
    }

    private static final int MAX_SUBST = 20;

    private static final int SUB_START_IDX = 0;
    private static final int SUB_END_IDX = SUB_START_IDX + 1;

    /**
     * This is a manual implementation of the following regex
     * "\\$\\{[^\\}\\$\u0020]+\\}". It can be 15x more efficient than
     * a regex matcher as demonstrated by HADOOP-11506. This is noticeable with
     * Hadoop apps building on the assumption Configuration#get is an O(1)
     * hash table lookup, especially when the eval is a long string.
     *
     * @param eval a string that may contain variables requiring expansion.
     * @return a 2-element int array res such that
     * eval.substring(res[0], res[1]) is "var" for the left-most occurrence of
     * ${var} in eval. If no variable is found -1, -1 is returned.
     */
    private static int[] findSubVariable(String eval) {
        int[] result = { -1, -1 };

        int matchStart;
        int leftBrace;

        // scanning for a brace first because it's less frequent than $
        // that can occur in nested class names
        //
        match_loop: for (matchStart = 1, leftBrace = eval.indexOf('{', matchStart);
                // minimum left brace position (follows '$')
                leftBrace > 0
                        // right brace of a smallest valid expression "${c}"
                        && leftBrace + "{c".length() < eval.length(); leftBrace = eval.indexOf('{', matchStart)) {
            int matchedLen = 0;
            if (eval.charAt(leftBrace - 1) == '$') {
                int subStart = leftBrace + 1; // after '{'
                for (int i = subStart; i < eval.length(); i++) {
                    switch (eval.charAt(i)) {
                    case '}':
                        if (matchedLen > 0) { // match
                            result[SUB_START_IDX] = subStart;
                            result[SUB_END_IDX] = subStart + matchedLen;
                            break match_loop;
                        }
                        // fall through to skip 1 char
                    case ' ':
                    case '$':
                        matchStart = i + 1;
                        continue match_loop;
                    default:
                        matchedLen++;
                    }
                }
                // scanned from "${"  to the end of eval, and no reset via ' ', '$':
                //    no match!
                break match_loop;
            } else {
                // not a start of a variable
                //
                matchStart = leftBrace + 1;
            }
        }
        return result;
    }

    /**
     * Attempts to repeatedly expand the value {@code expr} by replacing the
     * left-most substring of the form "${var}" in the following precedence order
     * <ol>
     *   <li>by the value of the environment variable "var" if defined</li>
     *   <li>by the value of the Java system property "var" if defined</li>
     *   <li>by the value of the configuration key "var" if defined</li>
     * </ol>
     *
     * If var is unbounded the current state of expansion "prefix${var}suffix" is
     * returned.
     * <p>
     * This function also detects self-referential substitutions, i.e.
     * <pre>
     *   {@code
     *   foo.bar = ${foo.bar}
     *   }
     * </pre>
     * If a cycle is detected then the original expr is returned. Loops
     * involving multiple substitutions are not detected.
     *
     * @param expr the literal value of a config key
     * @return null if expr is null, otherwise the value resulting from expanding
     * expr using the algorithm above.
     * @throws IllegalArgumentException when more than
     * {@link Configuration#MAX_SUBST} replacements are required
     */
    private String substituteVars(String expr) {
        if (expr == null) {
            return null;
        }
        String eval = expr;
        for (int s = 0; s < MAX_SUBST; s++) {
            final int[] varBounds = findSubVariable(eval);
            if (varBounds[SUB_START_IDX] == -1) {
                return eval;
            }
            final String var = eval.substring(varBounds[SUB_START_IDX], varBounds[SUB_END_IDX]);
            String val = null;
            if (!restrictSystemProps) {
                try {
                    if (var.startsWith("env.") && 4 < var.length()) {
                        String v = var.substring(4);
                        int i = 0;
                        for (; i < v.length(); i++) {
                            char c = v.charAt(i);
                            if (c == ':' && i < v.length() - 1 && v.charAt(i + 1) == '-') {
                                val = getenv(v.substring(0, i));
                                if (val == null || val.length() == 0) {
                                    val = v.substring(i + 2);
                                }
                                break;
                            } else if (c == '-') {
                                val = getenv(v.substring(0, i));
                                if (val == null) {
                                    val = v.substring(i + 1);
                                }
                                break;
                            }
                        }
                        if (i == v.length()) {
                            val = getenv(v);
                        }
                    } else {
                        val = getProperty(var);
                    }
                } catch (SecurityException se) {
                    LOG.warn("Unexpected SecurityException in Configuration", se);
                }
            }
            if (val == null) {
                val = getRaw(var);
            }
            if (val == null) {
                return eval; // return literal ${var}: var is unbound
            }

            final int dollar = varBounds[SUB_START_IDX] - "${".length();
            final int afterRightBrace = varBounds[SUB_END_IDX] + "}".length();
            final String refVar = eval.substring(dollar, afterRightBrace);

            // detect self-referential values
            if (val.contains(refVar)) {
                return expr; // return original expression if there is a loop
            }

            // substitute
            eval = eval.substring(0, dollar) + val + eval.substring(afterRightBrace);
        }
        throw new IllegalStateException("Variable substitution depth too large: " + MAX_SUBST + " " + expr);
    }

    String getenv(String name) {
        return System.getenv(name);
    }

    String getProperty(String key) {
        return System.getProperty(key);
    }

    /**
     * Get the value of the <code>name</code> property, <code>null</code> if
     * no such property exists. If the key is deprecated, it returns the value of
     * the first key which replaces the deprecated key and is not null.
     * 
     * Values are processed for <a href="#VariableExpansion">variable expansion</a> 
     * before being returned. 
     * 
     * @param name the property name, will be trimmed before get value.
     * @return the value of the <code>name</code> or its replacing property, 
     *         or null if no such property exists.
     */
    public String get(String name) {
        String[] names = handleDeprecation(deprecationContext.get(), name);
        String result = null;
        for (String n : names) {
            result = substituteVars(getProps().getProperty(n));
        }
        return result;
    }

    /**
     * Set Configuration to allow keys without values during setup.  Intended
     * for use during testing.
     *
     * @param val If true, will allow Configuration to store keys without values
     */
    @VisibleForTesting
    public void setAllowNullValueProperties(boolean val) {
        this.allowNullValueProperties = val;
    }

    public void setRestrictSystemProps(boolean val) {
        this.restrictSystemProps = val;
    }

    /**
     * Return existence of the <code>name</code> property, but only for
     * names which have no valid value, usually non-existent or commented
     * out in XML.
     *
     * @param name the property name
     * @return true if the property <code>name</code> exists without value
     */
    @VisibleForTesting
    public boolean onlyKeyExists(String name) {
        String[] names = handleDeprecation(deprecationContext.get(), name);
        for (String n : names) {
            if (getProps().getProperty(n, DEFAULT_STRING_CHECK).equals(DEFAULT_STRING_CHECK)) {
                return true;
            }
        }
        return false;
    }

    /**
     * Get the value of the <code>name</code> property as a trimmed <code>String</code>, 
     * <code>null</code> if no such property exists. 
     * If the key is deprecated, it returns the value of
     * the first key which replaces the deprecated key and is not null
     * 
     * Values are processed for <a href="#VariableExpansion">variable expansion</a> 
     * before being returned. 
     * 
     * @param name the property name.
     * @return the value of the <code>name</code> or its replacing property, 
     *         or null if no such property exists.
     */
    public String getTrimmed(String name) {
        String value = get(name);

        if (null == value) {
            return null;
        } else {
            return value.trim();
        }
    }

    /**
     * Get the value of the <code>name</code> property as a trimmed <code>String</code>, 
     * <code>defaultValue</code> if no such property exists. 
     * See @{Configuration#getTrimmed} for more details.
     * 
     * @param name          the property name.
     * @param defaultValue  the property default value.
     * @return              the value of the <code>name</code> or defaultValue
     *                      if it is not set.
     */
    public String getTrimmed(String name, String defaultValue) {
        String ret = getTrimmed(name);
        return ret == null ? defaultValue : ret;
    }

    /**
     * Get the value of the <code>name</code> property, without doing
     * <a href="#VariableExpansion">variable expansion</a>.If the key is 
     * deprecated, it returns the value of the first key which replaces 
     * the deprecated key and is not null.
     * 
     * @param name the property name.
     * @return the value of the <code>name</code> property or 
     *         its replacing property and null if no such property exists.
     */
    public String getRaw(String name) {
        String[] names = handleDeprecation(deprecationContext.get(), name);
        String result = null;
        for (String n : names) {
            result = getProps().getProperty(n);
        }
        return result;
    }

    /**
     * Returns alternative names (non-deprecated keys or previously-set deprecated keys)
     * for a given non-deprecated key.
     * If the given key is deprecated, return null.
     *
     * @param name property name.
     * @return alternative names.
     */
    private String[] getAlternativeNames(String name) {
        String altNames[] = null;
        DeprecatedKeyInfo keyInfo = null;
        DeprecationContext cur = deprecationContext.get();
        String depKey = cur.getReverseDeprecatedKeyMap().get(name);
        if (depKey != null) {
            keyInfo = cur.getDeprecatedKeyMap().get(depKey);
            if (keyInfo.newKeys.length > 0) {
                if (getProps().containsKey(depKey)) {
                    //if deprecated key is previously set explicitly
                    List<String> list = new ArrayList<String>();
                    list.addAll(Arrays.asList(keyInfo.newKeys));
                    list.add(depKey);
                    altNames = list.toArray(new String[list.size()]);
                } else {
                    altNames = keyInfo.newKeys;
                }
            }
        }
        return altNames;
    }

    /** 
     * Set the <code>value</code> of the <code>name</code> property. If 
     * <code>name</code> is deprecated or there is a deprecated name associated to it,
     * it sets the value to both names. Name will be trimmed before put into
     * configuration.
     * 
     * @param name property name.
     * @param value property value.
     */
    public void set(String name, String value) {
        set(name, value, null);
    }

    /** 
     * Set the <code>value</code> of the <code>name</code> property. If 
     * <code>name</code> is deprecated, it also sets the <code>value</code> to
     * the keys that replace the deprecated key. Name will be trimmed before put
     * into configuration.
     *
     * @param name property name.
     * @param value property value.
     * @param source the place that this configuration value came from 
     * (For debugging).
     * @throws IllegalArgumentException when the value or name is null.
     */
    public void set(String name, String value, String source) {
        Preconditions.checkArgument(name != null, "Property name must not be null");
        Preconditions.checkArgument(value != null, "The value of property %s must not be null", name);
        name = name.trim();
        DeprecationContext deprecations = deprecationContext.get();
        if (deprecations.getDeprecatedKeyMap().isEmpty()) {
            getProps();
        }
        getOverlay().setProperty(name, value);
        getProps().setProperty(name, value);
        String newSource = (source == null ? "programmatically" : source);

        if (!isDeprecated(name)) {
            putIntoUpdatingResource(name, new String[] { newSource });
            String[] altNames = getAlternativeNames(name);
            if (altNames != null) {
                for (String n : altNames) {
                    if (!n.equals(name)) {
                        getOverlay().setProperty(n, value);
                        getProps().setProperty(n, value);
                        putIntoUpdatingResource(n, new String[] { newSource });
                    }
                }
            }
        } else {
            String[] names = handleDeprecation(deprecationContext.get(), name);
            String altSource = "because " + name + " is deprecated";
            for (String n : names) {
                getOverlay().setProperty(n, value);
                getProps().setProperty(n, value);
                putIntoUpdatingResource(n, new String[] { altSource });
            }
        }
    }

    @VisibleForTesting
    void logDeprecation(String message) {
        LOG_DEPRECATION.info(message);
    }

    void logDeprecationOnce(String name, String source) {
        DeprecatedKeyInfo keyInfo = getDeprecatedKeyInfo(name);
        if (keyInfo != null && !keyInfo.getAndSetAccessed()) {
            LOG_DEPRECATION.info(keyInfo.getWarningMessage(name, source));
        }
    }

    /**
     * Unset a previously set property.
     */
    public synchronized void unset(String name) {
        String[] names = null;
        if (!isDeprecated(name)) {
            names = getAlternativeNames(name);
            if (names == null) {
                names = new String[] { name };
            }
        } else {
            names = handleDeprecation(deprecationContext.get(), name);
        }

        for (String n : names) {
            getOverlay().remove(n);
            getProps().remove(n);
        }
    }

    /**
     * Sets a property if it is currently unset.
     * @param name the property name
     * @param value the new value
     */
    public synchronized void setIfUnset(String name, String value) {
        if (get(name) == null) {
            set(name, value);
        }
    }

    private synchronized Properties getOverlay() {
        if (overlay == null) {
            overlay = new Properties();
        }
        return overlay;
    }

    /** 
     * Get the value of the <code>name</code>. If the key is deprecated,
     * it returns the value of the first key which replaces the deprecated key
     * and is not null.
     * If no such property exists,
     * then <code>defaultValue</code> is returned.
     * 
     * @param name property name, will be trimmed before get value.
     * @param defaultValue default value.
     * @return property value, or <code>defaultValue</code> if the property 
     *         doesn't exist.                    
     */
    public String get(String name, String defaultValue) {
        String[] names = handleDeprecation(deprecationContext.get(), name);
        String result = null;
        for (String n : names) {
            result = substituteVars(getProps().getProperty(n, defaultValue));
        }
        return result;
    }

    /** 
     * Get the value of the <code>name</code> property as an <code>int</code>.
     *   
     * If no such property exists, the provided default value is returned,
     * or if the specified value is not a valid <code>int</code>,
     * then an error is thrown.
     * 
     * @param name property name.
     * @param defaultValue default value.
     * @throws NumberFormatException when the value is invalid
     * @return property value as an <code>int</code>, 
     *         or <code>defaultValue</code>. 
     */
    public int getInt(String name, int defaultValue) {
        String valueString = getTrimmed(name);
        if (valueString == null)
            return defaultValue;
        String hexString = getHexDigits(valueString);
        if (hexString != null) {
            return Integer.parseInt(hexString, 16);
        }
        return Integer.parseInt(valueString);
    }

    /**
     * Get the value of the <code>name</code> property as a set of comma-delimited
     * <code>int</code> values.
     * 
     * If no such property exists, an empty array is returned.
     * 
     * @param name property name
     * @return property value interpreted as an array of comma-delimited
     *         <code>int</code> values
     */
    public int[] getInts(String name) {
        String[] strings = getTrimmedStrings(name);
        int[] ints = new int[strings.length];
        for (int i = 0; i < strings.length; i++) {
            ints[i] = Integer.parseInt(strings[i]);
        }
        return ints;
    }

    /** 
     * Set the value of the <code>name</code> property to an <code>int</code>.
     * 
     * @param name property name.
     * @param value <code>int</code> value of the property.
     */
    public void setInt(String name, int value) {
        set(name, Integer.toString(value));
    }

    /** 
     * Get the value of the <code>name</code> property as a <code>long</code>.  
     * If no such property exists, the provided default value is returned,
     * or if the specified value is not a valid <code>long</code>,
     * then an error is thrown.
     * 
     * @param name property name.
     * @param defaultValue default value.
     * @throws NumberFormatException when the value is invalid
     * @return property value as a <code>long</code>, 
     *         or <code>defaultValue</code>. 
     */
    public long getLong(String name, long defaultValue) {
        String valueString = getTrimmed(name);
        if (valueString == null)
            return defaultValue;
        String hexString = getHexDigits(valueString);
        if (hexString != null) {
            return Long.parseLong(hexString, 16);
        }
        return Long.parseLong(valueString);
    }

    /**
     * Get the value of the <code>name</code> property as a <code>long</code> or
     * human readable format. If no such property exists, the provided default
     * value is returned, or if the specified value is not a valid
     * <code>long</code> or human readable format, then an error is thrown. You
     * can use the following suffix (case insensitive): k(kilo), m(mega), g(giga),
     * t(tera), p(peta), e(exa)
     *
     * @param name property name.
     * @param defaultValue default value.
     * @throws NumberFormatException when the value is invalid
     * @return property value as a <code>long</code>,
     *         or <code>defaultValue</code>.
     */
    public long getLongBytes(String name, long defaultValue) {
        String valueString = getTrimmed(name);
        if (valueString == null)
            return defaultValue;
        return StringUtils.TraditionalBinaryPrefix.string2long(valueString);
    }

    private String getHexDigits(String value) {
        boolean negative = false;
        String str = value;
        String hexString = null;
        if (value.startsWith("-")) {
            negative = true;
            str = value.substring(1);
        }
        if (str.startsWith("0x") || str.startsWith("0X")) {
            hexString = str.substring(2);
            if (negative) {
                hexString = "-" + hexString;
            }
            return hexString;
        }
        return null;
    }

    /** 
     * Set the value of the <code>name</code> property to a <code>long</code>.
     * 
     * @param name property name.
     * @param value <code>long</code> value of the property.
     */
    public void setLong(String name, long value) {
        set(name, Long.toString(value));
    }

    /** 
     * Get the value of the <code>name</code> property as a <code>float</code>.  
     * If no such property exists, the provided default value is returned,
     * or if the specified value is not a valid <code>float</code>,
     * then an error is thrown.
     *
     * @param name property name.
     * @param defaultValue default value.
     * @throws NumberFormatException when the value is invalid
     * @return property value as a <code>float</code>, 
     *         or <code>defaultValue</code>. 
     */
    public float getFloat(String name, float defaultValue) {
        String valueString = getTrimmed(name);
        if (valueString == null)
            return defaultValue;
        return Float.parseFloat(valueString);
    }

    /**
     * Set the value of the <code>name</code> property to a <code>float</code>.
     * 
     * @param name property name.
     * @param value property value.
     */
    public void setFloat(String name, float value) {
        set(name, Float.toString(value));
    }

    /** 
     * Get the value of the <code>name</code> property as a <code>double</code>.  
     * If no such property exists, the provided default value is returned,
     * or if the specified value is not a valid <code>double</code>,
     * then an error is thrown.
     *
     * @param name property name.
     * @param defaultValue default value.
     * @throws NumberFormatException when the value is invalid
     * @return property value as a <code>double</code>, 
     *         or <code>defaultValue</code>. 
     */
    public double getDouble(String name, double defaultValue) {
        String valueString = getTrimmed(name);
        if (valueString == null)
            return defaultValue;
        return Double.parseDouble(valueString);
    }

    /**
     * Set the value of the <code>name</code> property to a <code>double</code>.
     * 
     * @param name property name.
     * @param value property value.
     */
    public void setDouble(String name, double value) {
        set(name, Double.toString(value));
    }

    /** 
     * Get the value of the <code>name</code> property as a <code>boolean</code>.  
     * If no such property is specified, or if the specified value is not a valid
     * <code>boolean</code>, then <code>defaultValue</code> is returned.
     * 
     * @param name property name.
     * @param defaultValue default value.
     * @return property value as a <code>boolean</code>, 
     *         or <code>defaultValue</code>. 
     */
    public boolean getBoolean(String name, boolean defaultValue) {
        String valueString = getTrimmed(name);
        if (null == valueString || valueString.isEmpty()) {
            return defaultValue;
        }

        if (StringUtils.equalsIgnoreCase("true", valueString))
            return true;
        else if (StringUtils.equalsIgnoreCase("false", valueString))
            return false;
        else
            return defaultValue;
    }

    /** 
     * Set the value of the <code>name</code> property to a <code>boolean</code>.
     * 
     * @param name property name.
     * @param value <code>boolean</code> value of the property.
     */
    public void setBoolean(String name, boolean value) {
        set(name, Boolean.toString(value));
    }

    /**
     * Set the given property, if it is currently unset.
     * @param name property name
     * @param value new value
     */
    public void setBooleanIfUnset(String name, boolean value) {
        setIfUnset(name, Boolean.toString(value));
    }

    /**
     * Set the value of the <code>name</code> property to the given type. This
     * is equivalent to <code>set(&lt;name&gt;, value.toString())</code>.
     * @param name property name
     * @param value new value
     */
    public <T extends Enum<T>> void setEnum(String name, T value) {
        set(name, value.toString());
    }

    /**
     * Return value matching this enumerated type.
     * Note that the returned value is trimmed by this method.
     * @param name Property name
     * @param defaultValue Value returned if no mapping exists
     * @throws IllegalArgumentException If mapping is illegal for the type
     * provided
     */
    public <T extends Enum<T>> T getEnum(String name, T defaultValue) {
        final String val = getTrimmed(name);
        return null == val ? defaultValue : Enum.valueOf(defaultValue.getDeclaringClass(), val);
    }

    enum ParsedTimeDuration {
        NS {
            TimeUnit unit() {
                return TimeUnit.NANOSECONDS;
            }

            String suffix() {
                return "ns";
            }
        },
        US {
            TimeUnit unit() {
                return TimeUnit.MICROSECONDS;
            }

            String suffix() {
                return "us";
            }
        },
        MS {
            TimeUnit unit() {
                return TimeUnit.MILLISECONDS;
            }

            String suffix() {
                return "ms";
            }
        },
        S {
            TimeUnit unit() {
                return TimeUnit.SECONDS;
            }

            String suffix() {
                return "s";
            }
        },
        M {
            TimeUnit unit() {
                return TimeUnit.MINUTES;
            }

            String suffix() {
                return "m";
            }
        },
        H {
            TimeUnit unit() {
                return TimeUnit.HOURS;
            }

            String suffix() {
                return "h";
            }
        },
        D {
            TimeUnit unit() {
                return TimeUnit.DAYS;
            }

            String suffix() {
                return "d";
            }
        };
        abstract TimeUnit unit();

        abstract String suffix();

        static ParsedTimeDuration unitFor(String s) {
            for (ParsedTimeDuration ptd : values()) {
                // iteration order is in decl order, so SECONDS matched last
                if (s.endsWith(ptd.suffix())) {
                    return ptd;
                }
            }
            return null;
        }

        static ParsedTimeDuration unitFor(TimeUnit unit) {
            for (ParsedTimeDuration ptd : values()) {
                if (ptd.unit() == unit) {
                    return ptd;
                }
            }
            return null;
        }
    }

    /**
     * Set the value of <code>name</code> to the given time duration. This
     * is equivalent to <code>set(&lt;name&gt;, value + &lt;time suffix&gt;)</code>.
     * @param name Property name
     * @param value Time duration
     * @param unit Unit of time
     */
    public void setTimeDuration(String name, long value, TimeUnit unit) {
        set(name, value + ParsedTimeDuration.unitFor(unit).suffix());
    }

    /**
     * Return time duration in the given time unit. Valid units are encoded in
     * properties as suffixes: nanoseconds (ns), microseconds (us), milliseconds
     * (ms), seconds (s), minutes (m), hours (h), and days (d).
     * @param name Property name
     * @param defaultValue Value returned if no mapping exists.
     * @param unit Unit to convert the stored property, if it exists.
     * @throws NumberFormatException If the property stripped of its unit is not
     *         a number
     */
    public long getTimeDuration(String name, long defaultValue, TimeUnit unit) {
        String vStr = get(name);
        if (null == vStr) {
            return defaultValue;
        } else {
            return getTimeDurationHelper(name, vStr, unit);
        }
    }

    public long getTimeDuration(String name, String defaultValue, TimeUnit unit) {
        String vStr = get(name);
        if (null == vStr) {
            return getTimeDurationHelper(name, defaultValue, unit);
        } else {
            return getTimeDurationHelper(name, vStr, unit);
        }
    }

    /**
     * Return time duration in the given time unit. Valid units are encoded in
     * properties as suffixes: nanoseconds (ns), microseconds (us), milliseconds
     * (ms), seconds (s), minutes (m), hours (h), and days (d).
     * @param name Property name
     * @param vStr The string value with time unit suffix to be converted.
     * @param unit Unit to convert the stored property, if it exists.
     */
    public long getTimeDurationHelper(String name, String vStr, TimeUnit unit) {
        vStr = vStr.trim();
        vStr = StringUtils.toLowerCase(vStr);
        ParsedTimeDuration vUnit = ParsedTimeDuration.unitFor(vStr);
        if (null == vUnit) {
            logDeprecation("No unit for " + name + "(" + vStr + ") assuming " + unit);
            vUnit = ParsedTimeDuration.unitFor(unit);
        } else {
            vStr = vStr.substring(0, vStr.lastIndexOf(vUnit.suffix()));
        }

        long raw = Long.parseLong(vStr);
        long converted = unit.convert(raw, vUnit.unit());
        if (vUnit.unit().convert(converted, unit) < raw) {
            logDeprecation("Possible loss of precision converting " + vStr + vUnit.suffix() + " to " + unit
                    + " for " + name);
        }
        return converted;
    }

    public long[] getTimeDurations(String name, TimeUnit unit) {
        String[] strings = getTrimmedStrings(name);
        long[] durations = new long[strings.length];
        for (int i = 0; i < strings.length; i++) {
            durations[i] = getTimeDurationHelper(name, strings[i], unit);
        }
        return durations;
    }

    /**
     * Gets the Storage Size from the config, or returns the defaultValue. The
     * unit of return value is specified in target unit.
     *
     * @param name - Key Name
     * @param defaultValue - Default Value -- e.g. 100MB
     * @param targetUnit - The units that we want result to be in.
     * @return double -- formatted in target Units
     */
    public double getStorageSize(String name, String defaultValue, StorageUnit targetUnit) {
        Preconditions.checkState(isNotBlank(name), "Key cannot be blank.");
        String vString = get(name);
        if (isBlank(vString)) {
            vString = defaultValue;
        }

        // Please note: There is a bit of subtlety here. If the user specifies
        // the default unit as "1GB", but the requested unit is MB, we will return
        // the format in MB even thought the default string is specified in GB.

        // Converts a string like "1GB" to to unit specified in targetUnit.

        StorageSize measure = StorageSize.parse(vString);
        return convertStorageUnit(measure.getValue(), measure.getUnit(), targetUnit);
    }

    /**
     * Gets storage size from a config file.
     *
     * @param name - Key to read.
     * @param defaultValue - The default value to return in case the key is
     * not present.
     * @param targetUnit - The Storage unit that should be used
     * for the return value.
     * @return - double value in the Storage Unit specified.
     */
    public double getStorageSize(String name, double defaultValue, StorageUnit targetUnit) {
        Preconditions.checkNotNull(targetUnit, "Conversion unit cannot be null.");
        Preconditions.checkState(isNotBlank(name), "Name cannot be blank.");
        String vString = get(name);
        if (isBlank(vString)) {
            return targetUnit.getDefault(defaultValue);
        }

        StorageSize measure = StorageSize.parse(vString);
        return convertStorageUnit(measure.getValue(), measure.getUnit(), targetUnit);

    }

    /**
     * Sets Storage Size for the specified key.
     *
     * @param name - Key to set.
     * @param value - The numeric value to set.
     * @param unit - Storage Unit to be used.
     */
    public void setStorageSize(String name, double value, StorageUnit unit) {
        set(name, value + unit.getShortName());
    }

    /**
     * convert the value from one storage unit to another.
     *
     * @param value - value
     * @param sourceUnit - Source unit to convert from
     * @param targetUnit - target unit.
     * @return double.
     */
    private double convertStorageUnit(double value, StorageUnit sourceUnit, StorageUnit targetUnit) {
        double byteValue = sourceUnit.toBytes(value);
        return targetUnit.fromBytes(byteValue);
    }

    /**
     * Get the value of the <code>name</code> property as a <code>Pattern</code>.
     * If no such property is specified, or if the specified value is not a valid
     * <code>Pattern</code>, then <code>DefaultValue</code> is returned.
     * Note that the returned value is NOT trimmed by this method.
     *
     * @param name property name
     * @param defaultValue default value
     * @return property value as a compiled Pattern, or defaultValue
     */
    public Pattern getPattern(String name, Pattern defaultValue) {
        String valString = get(name);
        if (null == valString || valString.isEmpty()) {
            return defaultValue;
        }
        try {
            return Pattern.compile(valString);
        } catch (PatternSyntaxException pse) {
            LOG.warn("Regular expression '" + valString + "' for property '" + name + "' not valid. Using default",
                    pse);
            return defaultValue;
        }
    }

    /**
     * Set the given property to <code>Pattern</code>.
     * If the pattern is passed as null, sets the empty pattern which results in
     * further calls to getPattern(...) returning the default value.
     *
     * @param name property name
     * @param pattern new value
     */
    public void setPattern(String name, Pattern pattern) {
        assert pattern != null : "Pattern cannot be null";
        set(name, pattern.pattern());
    }

    /**
     * Gets information about why a property was set.  Typically this is the 
     * path to the resource objects (file, URL, etc.) the property came from, but
     * it can also indicate that it was set programmatically, or because of the
     * command line.
     *
     * @param name - The property name to get the source of.
     * @return null - If the property or its source wasn't found. Otherwise, 
     * returns a list of the sources of the resource.  The older sources are
     * the first ones in the list.  So for example if a configuration is set from
     * the command line, and then written out to a file that is read back in the
     * first entry would indicate that it was set from the command line, while
     * the second one would indicate the file that the new configuration was read
     * in from.
     */
    @InterfaceStability.Unstable
    public synchronized String[] getPropertySources(String name) {
        if (properties == null) {
            // If properties is null, it means a resource was newly added
            // but the props were cleared so as to load it upon future
            // requests. So lets force a load by asking a properties list.
            getProps();
        }
        // Return a null right away if our properties still
        // haven't loaded or the resource mapping isn't defined
        if (properties == null || updatingResource == null) {
            return null;
        } else {
            String[] source = updatingResource.get(name);
            if (source == null) {
                return null;
            } else {
                return Arrays.copyOf(source, source.length);
            }
        }
    }

    /**
     * A class that represents a set of positive integer ranges. It parses 
     * strings of the form: "2-3,5,7-" where ranges are separated by comma and 
     * the lower/upper bounds are separated by dash. Either the lower or upper 
     * bound may be omitted meaning all values up to or over. So the string 
     * above means 2, 3, 5, and 7, 8, 9, ...
     */
    public static class IntegerRanges implements Iterable<Integer> {
        private static class Range {
            int start;
            int end;
        }

        private static class RangeNumberIterator implements Iterator<Integer> {
            Iterator<Range> internal;
            int at;
            int end;

            public RangeNumberIterator(List<Range> ranges) {
                if (ranges != null) {
                    internal = ranges.iterator();
                }
                at = -1;
                end = -2;
            }

            @Override
            public boolean hasNext() {
                if (at <= end) {
                    return true;
                } else if (internal != null) {
                    return internal.hasNext();
                }
                return false;
            }

            @Override
            public Integer next() {
                if (at <= end) {
                    at++;
                    return at - 1;
                } else if (internal != null) {
                    Range found = internal.next();
                    if (found != null) {
                        at = found.start;
                        end = found.end;
                        at++;
                        return at - 1;
                    }
                }
                return null;
            }

            @Override
            public void remove() {
                throw new UnsupportedOperationException();
            }
        };

        List<Range> ranges = new ArrayList<Range>();

        public IntegerRanges() {
        }

        public IntegerRanges(String newValue) {
            StringTokenizer itr = new StringTokenizer(newValue, ",");
            while (itr.hasMoreTokens()) {
                String rng = itr.nextToken().trim();
                String[] parts = rng.split("-", 3);
                if (parts.length < 1 || parts.length > 2) {
                    throw new IllegalArgumentException("integer range badly formed: " + rng);
                }
                Range r = new Range();
                r.start = convertToInt(parts[0], 0);
                if (parts.length == 2) {
                    r.end = convertToInt(parts[1], Integer.MAX_VALUE);
                } else {
                    r.end = r.start;
                }
                if (r.start > r.end) {
                    throw new IllegalArgumentException(
                            "IntegerRange from " + r.start + " to " + r.end + " is invalid");
                }
                ranges.add(r);
            }
        }

        /**
         * Convert a string to an int treating empty strings as the default value.
         * @param value the string value
         * @param defaultValue the value for if the string is empty
         * @return the desired integer
         */
        private static int convertToInt(String value, int defaultValue) {
            String trim = value.trim();
            if (trim.length() == 0) {
                return defaultValue;
            }
            return Integer.parseInt(trim);
        }

        /**
         * Is the given value in the set of ranges
         * @param value the value to check
         * @return is the value in the ranges?
         */
        public boolean isIncluded(int value) {
            for (Range r : ranges) {
                if (r.start <= value && value <= r.end) {
                    return true;
                }
            }
            return false;
        }

        /**
         * @return true if there are no values in this range, else false.
         */
        public boolean isEmpty() {
            return ranges == null || ranges.isEmpty();
        }

        @Override
        public String toString() {
            StringBuilder result = new StringBuilder();
            boolean first = true;
            for (Range r : ranges) {
                if (first) {
                    first = false;
                } else {
                    result.append(',');
                }
                result.append(r.start);
                result.append('-');
                result.append(r.end);
            }
            return result.toString();
        }

        /**
         * Get range start for the first integer range.
         * @return range start.
         */
        public int getRangeStart() {
            if (ranges == null || ranges.isEmpty()) {
                return -1;
            }
            Range r = ranges.get(0);
            return r.start;
        }

        @Override
        public Iterator<Integer> iterator() {
            return new RangeNumberIterator(ranges);
        }

    }

    /**
     * Parse the given attribute as a set of integer ranges
     * @param name the attribute name
     * @param defaultValue the default value if it is not set
     * @return a new set of ranges from the configured value
     */
    public IntegerRanges getRange(String name, String defaultValue) {
        return new IntegerRanges(get(name, defaultValue));
    }

    /** 
     * Get the comma delimited values of the <code>name</code> property as 
     * a collection of <code>String</code>s.  
     * If no such property is specified then empty collection is returned.
     * <p>
     * This is an optimized version of {@link #getStrings(String)}
     * 
     * @param name property name.
     * @return property value as a collection of <code>String</code>s. 
     */
    public Collection<String> getStringCollection(String name) {
        String valueString = get(name);
        return StringUtils.getStringCollection(valueString);
    }

    /** 
     * Get the comma delimited values of the <code>name</code> property as 
     * an array of <code>String</code>s.  
     * If no such property is specified then <code>null</code> is returned.
     * 
     * @param name property name.
     * @return property value as an array of <code>String</code>s, 
     *         or <code>null</code>. 
     */
    public String[] getStrings(String name) {
        String valueString = get(name);
        return StringUtils.getStrings(valueString);
    }

    /** 
     * Get the comma delimited values of the <code>name</code> property as 
     * an array of <code>String</code>s.  
     * If no such property is specified then default value is returned.
     * 
     * @param name property name.
     * @param defaultValue The default value
     * @return property value as an array of <code>String</code>s, 
     *         or default value. 
     */
    public String[] getStrings(String name, String... defaultValue) {
        String valueString = get(name);
        if (valueString == null) {
            return defaultValue;
        } else {
            return StringUtils.getStrings(valueString);
        }
    }

    /** 
     * Get the comma delimited values of the <code>name</code> property as 
     * a collection of <code>String</code>s, trimmed of the leading and trailing whitespace.  
     * If no such property is specified then empty <code>Collection</code> is returned.
     *
     * @param name property name.
     * @return property value as a collection of <code>String</code>s, or empty <code>Collection</code> 
     */
    public Collection<String> getTrimmedStringCollection(String name) {
        String valueString = get(name);
        if (null == valueString) {
            Collection<String> empty = new ArrayList<String>();
            return empty;
        }
        return StringUtils.getTrimmedStringCollection(valueString);
    }

    /** 
     * Get the comma delimited values of the <code>name</code> property as 
     * an array of <code>String</code>s, trimmed of the leading and trailing whitespace.
     * If no such property is specified then an empty array is returned.
     * 
     * @param name property name.
     * @return property value as an array of trimmed <code>String</code>s, 
     *         or empty array. 
     */
    public String[] getTrimmedStrings(String name) {
        String valueString = get(name);
        return StringUtils.getTrimmedStrings(valueString);
    }

    /** 
     * Get the comma delimited values of the <code>name</code> property as 
     * an array of <code>String</code>s, trimmed of the leading and trailing whitespace.
     * If no such property is specified then default value is returned.
     * 
     * @param name property name.
     * @param defaultValue The default value
     * @return property value as an array of trimmed <code>String</code>s, 
     *         or default value. 
     */
    public String[] getTrimmedStrings(String name, String... defaultValue) {
        String valueString = get(name);
        if (null == valueString) {
            return defaultValue;
        } else {
            return StringUtils.getTrimmedStrings(valueString);
        }
    }

    /** 
     * Set the array of string values for the <code>name</code> property as 
     * as comma delimited values.  
     * 
     * @param name property name.
     * @param values The values
     */
    public void setStrings(String name, String... values) {
        set(name, StringUtils.arrayToString(values));
    }

    /**
     * Get the value for a known password configuration element.
     * In order to enable the elimination of clear text passwords in config,
     * this method attempts to resolve the property name as an alias through
     * the CredentialProvider API and conditionally fallsback to config.
     * @param name property name
     * @return password
     */
    public char[] getPassword(String name) throws IOException {
        char[] pass = null;

        pass = getPasswordFromCredentialProviders(name);

        if (pass == null) {
            pass = getPasswordFromConfig(name);
        }

        return pass;
    }

    /**
     * Get the credential entry by name from a credential provider.
     *
     * Handle key deprecation.
     *
     * @param provider a credential provider
     * @param name alias of the credential
     * @return the credential entry or null if not found
     */
    private CredentialEntry getCredentialEntry(CredentialProvider provider, String name) throws IOException {
        CredentialEntry entry = provider.getCredentialEntry(name);
        if (entry != null) {
            return entry;
        }

        // The old name is stored in the credential provider.
        String oldName = getDeprecatedKey(name);
        if (oldName != null) {
            entry = provider.getCredentialEntry(oldName);
            if (entry != null) {
                logDeprecationOnce(oldName, provider.toString());
                return entry;
            }
        }

        // The name is deprecated.
        DeprecatedKeyInfo keyInfo = getDeprecatedKeyInfo(name);
        if (keyInfo != null && keyInfo.newKeys != null) {
            for (String newName : keyInfo.newKeys) {
                entry = provider.getCredentialEntry(newName);
                if (entry != null) {
                    logDeprecationOnce(name, null);
                    return entry;
                }
            }
        }

        return null;
    }

    /**
     * Try and resolve the provided element name as a credential provider
     * alias.
     * @param name alias of the provisioned credential
     * @return password or null if not found
     * @throws IOException
     */
    public char[] getPasswordFromCredentialProviders(String name) throws IOException {
        char[] pass = null;
        try {
            List<CredentialProvider> providers = CredentialProviderFactory.getProviders(this);

            if (providers != null) {
                for (CredentialProvider provider : providers) {
                    try {
                        CredentialEntry entry = getCredentialEntry(provider, name);
                        if (entry != null) {
                            pass = entry.getCredential();
                            break;
                        }
                    } catch (IOException ioe) {
                        throw new IOException("Can't get key " + name + " from key provider" + "of type: "
                                + provider.getClass().getName() + ".", ioe);
                    }
                }
            }
        } catch (IOException ioe) {
            throw new IOException("Configuration problem with provider path.", ioe);
        }

        return pass;
    }

    /**
     * Fallback to clear text passwords in configuration.
     * @param name
     * @return clear text password or null
     */
    protected char[] getPasswordFromConfig(String name) {
        char[] pass = null;
        if (getBoolean(CredentialProvider.CLEAR_TEXT_FALLBACK,
                CommonConfigurationKeysPublic.HADOOP_SECURITY_CREDENTIAL_CLEAR_TEXT_FALLBACK_DEFAULT)) {
            String passStr = get(name);
            if (passStr != null) {
                pass = passStr.toCharArray();
            }
        }
        return pass;
    }

    /**
     * Get the socket address for <code>hostProperty</code> as a
     * <code>InetSocketAddress</code>. If <code>hostProperty</code> is
     * <code>null</code>, <code>addressProperty</code> will be used. This
     * is useful for cases where we want to differentiate between host
     * bind address and address clients should use to establish connection.
     *
     * @param hostProperty bind host property name.
     * @param addressProperty address property name.
     * @param defaultAddressValue the default value
     * @param defaultPort the default port
     * @return InetSocketAddress
     */
    public InetSocketAddress getSocketAddr(String hostProperty, String addressProperty, String defaultAddressValue,
            int defaultPort) {

        InetSocketAddress bindAddr = getSocketAddr(addressProperty, defaultAddressValue, defaultPort);

        final String host = get(hostProperty);

        if (host == null || host.isEmpty()) {
            return bindAddr;
        }

        return NetUtils.createSocketAddr(host, bindAddr.getPort(), hostProperty);
    }

    /**
     * Get the socket address for <code>name</code> property as a
     * <code>InetSocketAddress</code>.
     * @param name property name.
     * @param defaultAddress the default value
     * @param defaultPort the default port
     * @return InetSocketAddress
     */
    public InetSocketAddress getSocketAddr(String name, String defaultAddress, int defaultPort) {
        final String address = getTrimmed(name, defaultAddress);
        return NetUtils.createSocketAddr(address, defaultPort, name);
    }

    /**
     * Set the socket address for the <code>name</code> property as
     * a <code>host:port</code>.
     */
    public void setSocketAddr(String name, InetSocketAddress addr) {
        set(name, NetUtils.getHostPortString(addr));
    }

    /**
     * Set the socket address a client can use to connect for the
     * <code>name</code> property as a <code>host:port</code>.  The wildcard
     * address is replaced with the local host's address. If the host and address
     * properties are configured the host component of the address will be combined
     * with the port component of the addr to generate the address.  This is to allow
     * optional control over which host name is used in multi-home bind-host
     * cases where a host can have multiple names
     * @param hostProperty the bind-host configuration name
     * @param addressProperty the service address configuration name
     * @param defaultAddressValue the service default address configuration value
     * @param addr InetSocketAddress of the service listener
     * @return InetSocketAddress for clients to connect
     */
    public InetSocketAddress updateConnectAddr(String hostProperty, String addressProperty,
            String defaultAddressValue, InetSocketAddress addr) {

        final String host = get(hostProperty);
        final String connectHostPort = getTrimmed(addressProperty, defaultAddressValue);

        if (host == null || host.isEmpty() || connectHostPort == null || connectHostPort.isEmpty()) {
            //not our case, fall back to original logic
            return updateConnectAddr(addressProperty, addr);
        }

        final String connectHost = connectHostPort.split(":")[0];
        // Create connect address using client address hostname and server port.
        return updateConnectAddr(addressProperty, NetUtils.createSocketAddrForHost(connectHost, addr.getPort()));
    }

    /**
     * Set the socket address a client can use to connect for the
     * <code>name</code> property as a <code>host:port</code>.  The wildcard
     * address is replaced with the local host's address.
     * @param name property name.
     * @param addr InetSocketAddress of a listener to store in the given property
     * @return InetSocketAddress for clients to connect
     */
    public InetSocketAddress updateConnectAddr(String name, InetSocketAddress addr) {
        final InetSocketAddress connectAddr = NetUtils.getConnectAddress(addr);
        setSocketAddr(name, connectAddr);
        return connectAddr;
    }

    /**
     * Load a class by name.
     * 
     * @param name the class name.
     * @return the class object.
     * @throws ClassNotFoundException if the class is not found.
     */
    public Class<?> getClassByName(String name) throws ClassNotFoundException {
        Class<?> ret = getClassByNameOrNull(name);
        if (ret == null) {
            throw new ClassNotFoundException("Class " + name + " not found");
        }
        return ret;
    }

    /**
     * Load a class by name, returning null rather than throwing an exception
     * if it couldn't be loaded. This is to avoid the overhead of creating
     * an exception.
     * 
     * @param name the class name
     * @return the class object, or null if it could not be found.
     */
    public Class<?> getClassByNameOrNull(String name) {
        Map<String, WeakReference<Class<?>>> map;

        synchronized (CACHE_CLASSES) {
            map = CACHE_CLASSES.get(classLoader);
            if (map == null) {
                map = Collections.synchronizedMap(new WeakHashMap<String, WeakReference<Class<?>>>());
                CACHE_CLASSES.put(classLoader, map);
            }
        }

        Class<?> clazz = null;
        WeakReference<Class<?>> ref = map.get(name);
        if (ref != null) {
            clazz = ref.get();
        }

        if (clazz == null) {
            try {
                clazz = Class.forName(name, true, classLoader);
            } catch (ClassNotFoundException e) {
                // Leave a marker that the class isn't found
                map.put(name, new WeakReference<Class<?>>(NEGATIVE_CACHE_SENTINEL));
                return null;
            }
            // two putters can race here, but they'll put the same class
            map.put(name, new WeakReference<Class<?>>(clazz));
            return clazz;
        } else if (clazz == NEGATIVE_CACHE_SENTINEL) {
            return null; // not found
        } else {
            // cache hit
            return clazz;
        }
    }

    /** 
     * Get the value of the <code>name</code> property
     * as an array of <code>Class</code>.
     * The value of the property specifies a list of comma separated class names.  
     * If no such property is specified, then <code>defaultValue</code> is 
     * returned.
     * 
     * @param name the property name.
     * @param defaultValue default value.
     * @return property value as a <code>Class[]</code>, 
     *         or <code>defaultValue</code>. 
     */
    public Class<?>[] getClasses(String name, Class<?>... defaultValue) {
        String valueString = getRaw(name);
        if (null == valueString) {
            return defaultValue;
        }
        String[] classnames = getTrimmedStrings(name);
        try {
            Class<?>[] classes = new Class<?>[classnames.length];
            for (int i = 0; i < classnames.length; i++) {
                classes[i] = getClassByName(classnames[i]);
            }
            return classes;
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        }
    }

    /** 
     * Get the value of the <code>name</code> property as a <code>Class</code>.  
     * If no such property is specified, then <code>defaultValue</code> is 
     * returned.
     * 
     * @param name the class name.
     * @param defaultValue default value.
     * @return property value as a <code>Class</code>, 
     *         or <code>defaultValue</code>. 
     */
    public Class<?> getClass(String name, Class<?> defaultValue) {
        String valueString = getTrimmed(name);
        if (valueString == null)
            return defaultValue;
        try {
            return getClassByName(valueString);
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        }
    }

    /** 
     * Get the value of the <code>name</code> property as a <code>Class</code>
     * implementing the interface specified by <code>xface</code>.
     *   
     * If no such property is specified, then <code>defaultValue</code> is 
     * returned.
     * 
     * An exception is thrown if the returned class does not implement the named
     * interface. 
     * 
     * @param name the class name.
     * @param defaultValue default value.
     * @param xface the interface implemented by the named class.
     * @return property value as a <code>Class</code>, 
     *         or <code>defaultValue</code>.
     */
    public <U> Class<? extends U> getClass(String name, Class<? extends U> defaultValue, Class<U> xface) {
        try {
            Class<?> theClass = getClass(name, defaultValue);
            if (theClass != null && !xface.isAssignableFrom(theClass))
                throw new RuntimeException(theClass + " not " + xface.getName());
            else if (theClass != null)
                return theClass.asSubclass(xface);
            else
                return null;
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * Get the value of the <code>name</code> property as a <code>List</code>
     * of objects implementing the interface specified by <code>xface</code>.
     * 
     * An exception is thrown if any of the classes does not exist, or if it does
     * not implement the named interface.
     * 
     * @param name the property name.
     * @param xface the interface implemented by the classes named by
     *        <code>name</code>.
     * @return a <code>List</code> of objects implementing <code>xface</code>.
     */
    @SuppressWarnings("unchecked")
    public <U> List<U> getInstances(String name, Class<U> xface) {
        List<U> ret = new ArrayList<U>();
        Class<?>[] classes = getClasses(name);
        for (Class<?> cl : classes) {
            if (!xface.isAssignableFrom(cl)) {
                throw new RuntimeException(cl + " does not implement " + xface);
            }
            ret.add((U) ReflectionUtils.newInstance(cl, this));
        }
        return ret;
    }

    /** 
     * Set the value of the <code>name</code> property to the name of a 
     * <code>theClass</code> implementing the given interface <code>xface</code>.
     * 
     * An exception is thrown if <code>theClass</code> does not implement the 
     * interface <code>xface</code>. 
     * 
     * @param name property name.
     * @param theClass property value.
     * @param xface the interface implemented by the named class.
     */
    public void setClass(String name, Class<?> theClass, Class<?> xface) {
        if (!xface.isAssignableFrom(theClass))
            throw new RuntimeException(theClass + " not " + xface.getName());
        set(name, theClass.getName());
    }

    /** 
     * Get a local file under a directory named by <i>dirsProp</i> with
     * the given <i>path</i>.  If <i>dirsProp</i> contains multiple directories,
     * then one is chosen based on <i>path</i>'s hash code.  If the selected
     * directory does not exist, an attempt is made to create it.
     * 
     * @param dirsProp directory in which to locate the file.
     * @param path file-path.
     * @return local file under the directory with the given path.
     */
    public Path getLocalPath(String dirsProp, String path) throws IOException {
        String[] dirs = getTrimmedStrings(dirsProp);
        int hashCode = path.hashCode();
        FileSystem fs = FileSystem.getLocal(this);
        for (int i = 0; i < dirs.length; i++) { // try each local dir
            int index = (hashCode + i & Integer.MAX_VALUE) % dirs.length;
            Path file = new Path(dirs[index], path);
            Path dir = file.getParent();
            if (fs.mkdirs(dir) || fs.exists(dir)) {
                return file;
            }
        }
        LOG.warn("Could not make " + path + " in local directories from " + dirsProp);
        for (int i = 0; i < dirs.length; i++) {
            int index = (hashCode + i & Integer.MAX_VALUE) % dirs.length;
            LOG.warn(dirsProp + "[" + index + "]=" + dirs[index]);
        }
        throw new IOException("No valid local directories in property: " + dirsProp);
    }

    /** 
     * Get a local file name under a directory named in <i>dirsProp</i> with
     * the given <i>path</i>.  If <i>dirsProp</i> contains multiple directories,
     * then one is chosen based on <i>path</i>'s hash code.  If the selected
     * directory does not exist, an attempt is made to create it.
     * 
     * @param dirsProp directory in which to locate the file.
     * @param path file-path.
     * @return local file under the directory with the given path.
     */
    public File getFile(String dirsProp, String path) throws IOException {
        String[] dirs = getTrimmedStrings(dirsProp);
        int hashCode = path.hashCode();
        for (int i = 0; i < dirs.length; i++) { // try each local dir
            int index = (hashCode + i & Integer.MAX_VALUE) % dirs.length;
            File file = new File(dirs[index], path);
            File dir = file.getParentFile();
            if (dir.exists() || dir.mkdirs()) {
                return file;
            }
        }
        throw new IOException("No valid local directories in property: " + dirsProp);
    }

    /** 
     * Get the {@link URL} for the named resource.
     * 
     * @param name resource name.
     * @return the url for the named resource.
     */
    public URL getResource(String name) {
        return classLoader.getResource(name);
    }

    /** 
     * Get an input stream attached to the configuration resource with the
     * given <code>name</code>.
     * 
     * @param name configuration resource name.
     * @return an input stream attached to the resource.
     */
    public InputStream getConfResourceAsInputStream(String name) {
        try {
            URL url = getResource(name);

            if (url == null) {
                LOG.info(name + " not found");
                return null;
            } else {
                LOG.info("found resource " + name + " at " + url);
            }

            return url.openStream();
        } catch (Exception e) {
            return null;
        }
    }

    /** 
     * Get a {@link Reader} attached to the configuration resource with the
     * given <code>name</code>.
     * 
     * @param name configuration resource name.
     * @return a reader attached to the resource.
     */
    public Reader getConfResourceAsReader(String name) {
        try {
            URL url = getResource(name);

            if (url == null) {
                LOG.info(name + " not found");
                return null;
            } else {
                LOG.info("found resource " + name + " at " + url);
            }

            return new InputStreamReader(url.openStream(), Charsets.UTF_8);
        } catch (Exception e) {
            return null;
        }
    }

    /**
     * Get the set of parameters marked final.
     *
     * @return final parameter set.
     */
    public Set<String> getFinalParameters() {
        Set<String> setFinalParams = Collections.newSetFromMap(new ConcurrentHashMap<String, Boolean>());
        setFinalParams.addAll(finalParameters);
        return setFinalParams;
    }

    protected synchronized Properties getProps() {
        if (properties == null) {
            properties = new Properties();
            Map<String, String[]> backup = updatingResource != null
                    ? new ConcurrentHashMap<String, String[]>(updatingResource)
                    : null;
            loadResources(properties, resources, quietmode);

            if (overlay != null) {
                properties.putAll(overlay);
                if (backup != null) {
                    for (Map.Entry<Object, Object> item : overlay.entrySet()) {
                        String key = (String) item.getKey();
                        String[] source = backup.get(key);
                        if (source != null) {
                            updatingResource.put(key, source);
                        }
                    }
                }
            }
        }
        return properties;
    }

    /**
     * Return the number of keys in the configuration.
     *
     * @return number of keys in the configuration.
     */
    public int size() {
        return getProps().size();
    }

    /**
     * Clears all keys from the configuration.
     */
    public void clear() {
        getProps().clear();
        getOverlay().clear();
    }

    /**
     * Get an {@link Iterator} to go through the list of <code>String</code> 
     * key-value pairs in the configuration.
     * 
     * @return an iterator over the entries.
     */
    @Override
    public Iterator<Map.Entry<String, String>> iterator() {
        // Get a copy of just the string to string pairs. After the old object
        // methods that allow non-strings to be put into configurations are removed,
        // we could replace properties with a Map<String,String> and get rid of this
        // code.
        Map<String, String> result = new HashMap<String, String>();
        for (Map.Entry<Object, Object> item : getProps().entrySet()) {
            if (item.getKey() instanceof String && item.getValue() instanceof String) {
                result.put((String) item.getKey(), (String) item.getValue());
            }
        }
        return result.entrySet().iterator();
    }

    /**
     * Constructs a mapping of configuration and includes all properties that
     * start with the specified configuration prefix.  Property names in the
     * mapping are trimmed to remove the configuration prefix.
     *
     * @param confPrefix configuration prefix
     * @return mapping of configuration properties with prefix stripped
     */
    public Map<String, String> getPropsWithPrefix(String confPrefix) {
        Properties props = getProps();
        Map<String, String> configMap = new HashMap<>();
        for (String name : props.stringPropertyNames()) {
            if (name.startsWith(confPrefix)) {
                String value = get(name);
                String keyName = name.substring(confPrefix.length());
                configMap.put(keyName, value);
            }
        }
        return configMap;
    }

    private XMLStreamReader parse(URL url, boolean restricted) throws IOException, XMLStreamException {
        if (!quietmode) {
            if (LOG.isDebugEnabled()) {
                LOG.debug("parsing URL " + url);
            }
        }
        if (url == null) {
            return null;
        }

        URLConnection connection = url.openConnection();
        if (connection instanceof JarURLConnection) {
            // Disable caching for JarURLConnection to avoid sharing JarFile
            // with other users.
            connection.setUseCaches(false);
        }
        return parse(connection.getInputStream(), url.toString(), restricted);
    }

    private XMLStreamReader parse(InputStream is, String systemIdStr, boolean restricted)
            throws IOException, XMLStreamException {
        if (!quietmode) {
            LOG.debug("parsing input stream " + is);
        }
        if (is == null) {
            return null;
        }
        SystemId systemId = SystemId.construct(systemIdStr);
        ReaderConfig readerConfig = XML_INPUT_FACTORY.createPrivateConfig();
        if (restricted) {
            readerConfig.setProperty(XMLInputFactory.SUPPORT_DTD, false);
        }
        return XML_INPUT_FACTORY.createSR(readerConfig, systemId,
                StreamBootstrapper.getInstance(null, systemId, is), false, true);
    }

    private void loadResources(Properties properties, ArrayList<Resource> resources, boolean quiet) {
        if (loadDefaults) {
            for (String resource : defaultResources) {
                loadResource(properties, new Resource(resource, false), quiet);
            }
        }

        for (int i = 0; i < resources.size(); i++) {
            Resource ret = loadResource(properties, resources.get(i), quiet);
            if (ret != null) {
                resources.set(i, ret);
            }
        }
        this.addTags(properties);
    }

    private Resource loadResource(Properties properties, Resource wrapper, boolean quiet) {
        String name = UNKNOWN_RESOURCE;
        try {
            Object resource = wrapper.getResource();
            name = wrapper.getName();
            boolean returnCachedProperties = false;

            if (resource instanceof InputStream) {
                returnCachedProperties = true;
            } else if (resource instanceof Properties) {
                overlay(properties, (Properties) resource);
            }

            XMLStreamReader2 reader = getStreamReader(wrapper, quiet);
            if (reader == null) {
                if (quiet) {
                    return null;
                }
                throw new RuntimeException(resource + " not found");
            }
            Properties toAddTo = properties;
            if (returnCachedProperties) {
                toAddTo = new Properties();
            }

            List<ParsedItem> items = new Parser(reader, wrapper, quiet).parse();
            for (ParsedItem item : items) {
                loadProperty(toAddTo, item.name, item.key, item.value, item.isFinal, item.sources);
            }
            reader.close();

            if (returnCachedProperties) {
                overlay(properties, toAddTo);
                return new Resource(toAddTo, name, wrapper.isParserRestricted());
            }
            return null;
        } catch (IOException e) {
            LOG.error("error parsing conf " + name, e);
            throw new RuntimeException(e);
        } catch (XMLStreamException e) {
            LOG.error("error parsing conf " + name, e);
            throw new RuntimeException(e);
        }
    }

    private XMLStreamReader2 getStreamReader(Resource wrapper, boolean quiet)
            throws XMLStreamException, IOException {
        Object resource = wrapper.getResource();
        boolean isRestricted = wrapper.isParserRestricted();
        XMLStreamReader2 reader = null;
        if (resource instanceof URL) { // an URL resource
            reader = (XMLStreamReader2) parse((URL) resource, isRestricted);
        } else if (resource instanceof String) { // a CLASSPATH resource
            URL url = getResource((String) resource);
            reader = (XMLStreamReader2) parse(url, isRestricted);
        } else if (resource instanceof Path) { // a file resource
            // Can't use FileSystem API or we get an infinite loop
            // since FileSystem uses Configuration API.  Use java.io.File instead.
            File file = new File(((Path) resource).toUri().getPath()).getAbsoluteFile();
            if (file.exists()) {
                if (!quiet) {
                    LOG.debug("parsing File " + file);
                }
                reader = (XMLStreamReader2) parse(new BufferedInputStream(new FileInputStream(file)),
                        ((Path) resource).toString(), isRestricted);
            }
        } else if (resource instanceof InputStream) {
            reader = (XMLStreamReader2) parse((InputStream) resource, null, isRestricted);
        }
        return reader;
    }

    private static class ParsedItem {
        String name;
        String key;
        String value;
        boolean isFinal;
        String[] sources;

        ParsedItem(String name, String key, String value, boolean isFinal, String[] sources) {
            this.name = name;
            this.key = key;
            this.value = value;
            this.isFinal = isFinal;
            this.sources = sources;
        }
    }

    /**
     * Parser to consume SAX stream of XML elements from a Configuration.
     */
    private class Parser {
        private final XMLStreamReader2 reader;
        private final Resource wrapper;
        private final String name;
        private final String[] nameSingletonArray;
        private final boolean isRestricted;
        private final boolean quiet;

        DeprecationContext deprecations = deprecationContext.get();

        private StringBuilder token = new StringBuilder();
        private String confName = null;
        private String confValue = null;
        private String confInclude = null;
        private String confTag = null;
        private boolean confFinal = false;
        private boolean fallbackAllowed = false;
        private boolean fallbackEntered = false;
        private boolean parseToken = false;
        private List<String> confSource = new ArrayList<>();
        private List<ParsedItem> results = new ArrayList<>();

        Parser(XMLStreamReader2 reader, Resource wrapper, boolean quiet) {
            this.reader = reader;
            this.wrapper = wrapper;
            this.name = wrapper.getName();
            this.nameSingletonArray = new String[] { name };
            this.isRestricted = wrapper.isParserRestricted();
            this.quiet = quiet;

        }

        List<ParsedItem> parse() throws IOException, XMLStreamException {
            while (reader.hasNext()) {
                parseNext();
            }
            return results;
        }

        private void handleStartElement() throws XMLStreamException, IOException {
            switch (reader.getLocalName()) {
            case "property":
                handleStartProperty();
                break;

            case "name":
            case "value":
            case "final":
            case "source":
            case "tag":
                parseToken = true;
                token.setLength(0);
                break;
            case "include":
                handleInclude();
                break;
            case "fallback":
                fallbackEntered = true;
                break;
            case "configuration":
                break;
            default:
                break;
            }
        }

        private void handleStartProperty() {
            confName = null;
            confValue = null;
            confFinal = false;
            confTag = null;
            confSource.clear();

            // First test for short format configuration
            int attrCount = reader.getAttributeCount();
            for (int i = 0; i < attrCount; i++) {
                String propertyAttr = reader.getAttributeLocalName(i);
                if ("name".equals(propertyAttr)) {
                    confName = StringInterner.weakIntern(reader.getAttributeValue(i));
                } else if ("value".equals(propertyAttr)) {
                    confValue = StringInterner.weakIntern(reader.getAttributeValue(i));
                } else if ("final".equals(propertyAttr)) {
                    confFinal = "true".equals(reader.getAttributeValue(i));
                } else if ("source".equals(propertyAttr)) {
                    confSource.add(StringInterner.weakIntern(reader.getAttributeValue(i)));
                } else if ("tag".equals(propertyAttr)) {
                    confTag = StringInterner.weakIntern(reader.getAttributeValue(i));
                }
            }
        }

        private void handleInclude() throws XMLStreamException, IOException {
            // Determine href for xi:include
            confInclude = null;
            int attrCount = reader.getAttributeCount();
            List<ParsedItem> items;
            for (int i = 0; i < attrCount; i++) {
                String attrName = reader.getAttributeLocalName(i);
                if ("href".equals(attrName)) {
                    confInclude = reader.getAttributeValue(i);
                }
            }
            if (confInclude == null) {
                return;
            }
            if (isRestricted) {
                throw new RuntimeException("Error parsing resource " + wrapper
                        + ": XInclude is not supported for restricted resources");
            }
            // Determine if the included resource is a classpath resource
            // otherwise fallback to a file resource
            // xi:include are treated as inline and retain current source
            URL include = getResource(confInclude);
            if (include != null) {
                Resource classpathResource = new Resource(include, name, wrapper.isParserRestricted());
                // This is only called recursively while the lock is already held
                // by this thread, but synchronizing avoids a findbugs warning.
                synchronized (Configuration.this) {
                    XMLStreamReader2 includeReader = getStreamReader(classpathResource, quiet);
                    if (includeReader == null) {
                        throw new RuntimeException(classpathResource + " not found");
                    }
                    items = new Parser(includeReader, classpathResource, quiet).parse();
                }
            } else {
                URL url;
                try {
                    url = new URL(confInclude);
                    url.openConnection().connect();
                } catch (IOException ioe) {
                    File href = new File(confInclude);
                    if (!href.isAbsolute()) {
                        // Included resources are relative to the current resource
                        File baseFile = new File(name).getParentFile();
                        href = new File(baseFile, href.getPath());
                    }
                    if (!href.exists()) {
                        // Resource errors are non-fatal iff there is 1 xi:fallback
                        fallbackAllowed = true;
                        return;
                    }
                    url = href.toURI().toURL();
                }
                Resource uriResource = new Resource(url, name, wrapper.isParserRestricted());
                // This is only called recursively while the lock is already held
                // by this thread, but synchronizing avoids a findbugs warning.
                synchronized (Configuration.this) {
                    XMLStreamReader2 includeReader = getStreamReader(uriResource, quiet);
                    if (includeReader == null) {
                        throw new RuntimeException(uriResource + " not found");
                    }
                    items = new Parser(includeReader, uriResource, quiet).parse();
                }
            }
            results.addAll(items);
        }

        void handleEndElement() throws IOException {
            String tokenStr = token.toString();
            switch (reader.getLocalName()) {
            case "name":
                if (token.length() > 0) {
                    confName = StringInterner.weakIntern(tokenStr.trim());
                }
                break;
            case "value":
                if (token.length() > 0) {
                    confValue = StringInterner.weakIntern(tokenStr);
                }
                break;
            case "final":
                confFinal = "true".equals(tokenStr);
                break;
            case "source":
                confSource.add(StringInterner.weakIntern(tokenStr));
                break;
            case "tag":
                if (token.length() > 0) {
                    confTag = StringInterner.weakIntern(tokenStr);
                }
                break;
            case "include":
                if (fallbackAllowed && !fallbackEntered) {
                    throw new IOException("Fetch fail on include for '" + confInclude
                            + "' with no fallback while loading '" + name + "'");
                }
                fallbackAllowed = false;
                fallbackEntered = false;
                break;
            case "property":
                handleEndProperty();
                break;
            default:
                break;
            }
        }

        void handleEndProperty() {
            if (confName == null || (!fallbackAllowed && fallbackEntered)) {
                return;
            }
            String[] confSourceArray;
            if (confSource.isEmpty()) {
                confSourceArray = nameSingletonArray;
            } else {
                confSource.add(name);
                confSourceArray = confSource.toArray(new String[confSource.size()]);
            }

            // Read tags and put them in propertyTagsMap
            if (confTag != null) {
                readTagFromConfig(confTag, confName, confValue, confSourceArray);
            }

            DeprecatedKeyInfo keyInfo = deprecations.getDeprecatedKeyMap().get(confName);

            if (keyInfo != null) {
                keyInfo.clearAccessed();
                for (String key : keyInfo.newKeys) {
                    // update new keys with deprecated key's value
                    results.add(new ParsedItem(name, key, confValue, confFinal, confSourceArray));
                }
            } else {
                results.add(new ParsedItem(name, confName, confValue, confFinal, confSourceArray));
            }
        }

        void parseNext() throws IOException, XMLStreamException {
            switch (reader.next()) {
            case XMLStreamConstants.START_ELEMENT:
                handleStartElement();
                break;
            case XMLStreamConstants.CHARACTERS:
                if (parseToken) {
                    char[] text = reader.getTextCharacters();
                    token.append(text, reader.getTextStart(), reader.getTextLength());
                }
                break;
            case XMLStreamConstants.END_ELEMENT:
                handleEndElement();
                break;
            default:
                break;
            }
        }
    }

    /**
     * Add tags defined in HADOOP_TAGS_SYSTEM, HADOOP_TAGS_CUSTOM.
     * @param prop
     */
    public void addTags(Properties prop) {
        // Get all system tags
        try {
            if (prop.containsKey(CommonConfigurationKeys.HADOOP_TAGS_SYSTEM)) {
                String systemTags = prop.getProperty(CommonConfigurationKeys.HADOOP_TAGS_SYSTEM);
                TAGS.addAll(Arrays.asList(systemTags.split(",")));
            }
            // Get all custom tags
            if (prop.containsKey(CommonConfigurationKeys.HADOOP_TAGS_CUSTOM)) {
                String customTags = prop.getProperty(CommonConfigurationKeys.HADOOP_TAGS_CUSTOM);
                TAGS.addAll(Arrays.asList(customTags.split(",")));
            }

            if (prop.containsKey(CommonConfigurationKeys.HADOOP_SYSTEM_TAGS)) {
                String systemTags = prop.getProperty(CommonConfigurationKeys.HADOOP_SYSTEM_TAGS);
                TAGS.addAll(Arrays.asList(systemTags.split(",")));
            }
            // Get all custom tags
            if (prop.containsKey(CommonConfigurationKeys.HADOOP_CUSTOM_TAGS)) {
                String customTags = prop.getProperty(CommonConfigurationKeys.HADOOP_CUSTOM_TAGS);
                TAGS.addAll(Arrays.asList(customTags.split(",")));
            }

        } catch (Exception ex) {
            LOG.trace("Error adding tags in configuration", ex);
        }

    }

    /**
     * Read the values passed as tags and store them in a
     * map for later retrieval.
     * @param attributeValue
     * @param confName
     * @param confValue
     * @param confSource
     */
    private void readTagFromConfig(String attributeValue, String confName, String confValue, String[] confSource) {
        for (String tagStr : attributeValue.split(",")) {
            try {
                tagStr = tagStr.trim();
                // Handle property with no/null value
                if (confValue == null) {
                    confValue = "";
                }
                if (propertyTagsMap.containsKey(tagStr)) {
                    propertyTagsMap.get(tagStr).setProperty(confName, confValue);
                } else {
                    Properties props = new Properties();
                    props.setProperty(confName, confValue);
                    propertyTagsMap.put(tagStr, props);
                }
            } catch (Exception ex) {
                // Log the exception at trace level.
                LOG.trace("Tag '{}' for property:{} Source:{}", tagStr, confName, confSource, ex);
            }
        }
    }

    private void overlay(Properties to, Properties from) {
        for (Entry<Object, Object> entry : from.entrySet()) {
            to.put(entry.getKey(), entry.getValue());
        }
    }

    private void loadProperty(Properties properties, String name, String attr, String value, boolean finalParameter,
            String[] source) {
        if (value != null || allowNullValueProperties) {
            if (value == null) {
                value = DEFAULT_STRING_CHECK;
            }
            if (!finalParameters.contains(attr)) {
                properties.setProperty(attr, value);
                if (source != null) {
                    putIntoUpdatingResource(attr, source);
                }
            } else {
                // This is a final parameter so check for overrides.
                checkForOverride(this.properties, name, attr, value);
                if (this.properties != properties) {
                    checkForOverride(properties, name, attr, value);
                }
            }
        }
        if (finalParameter && attr != null) {
            finalParameters.add(attr);
        }
    }

    /**
     * Print a warning if a property with a given name already exists with a
     * different value
     */
    private void checkForOverride(Properties properties, String name, String attr, String value) {
        String propertyValue = properties.getProperty(attr);
        if (propertyValue != null && !propertyValue.equals(value)) {
            LOG.warn(name + ":an attempt to override final parameter: " + attr + ";  Ignoring.");
        }
    }

    /** 
     * Write out the non-default properties in this configuration to the given
     * {@link OutputStream} using UTF-8 encoding.
     * 
     * @param out the output stream to write to.
     */
    public void writeXml(OutputStream out) throws IOException {
        writeXml(new OutputStreamWriter(out, "UTF-8"));
    }

    public void writeXml(Writer out) throws IOException {
        writeXml(null, out);
    }

    /**
     * Write out the non-default properties in this configuration to the
     * given {@link Writer}.
     *
     * <li>
     * When property name is not empty and the property exists in the
     * configuration, this method writes the property and its attributes
     * to the {@link Writer}.
     * </li>
     * <p>
     *
     * <li>
     * When property name is null or empty, this method writes all the
     * configuration properties and their attributes to the {@link Writer}.
     * </li>
     * <p>
     *
     * <li>
     * When property name is not empty but the property doesn't exist in
     * the configuration, this method throws an {@link IllegalArgumentException}.
     * </li>
     * <p>
     * @param out the writer to write to.
     */
    public void writeXml(String propertyName, Writer out) throws IOException, IllegalArgumentException {
        Document doc = asXmlDocument(propertyName);

        try {
            DOMSource source = new DOMSource(doc);
            StreamResult result = new StreamResult(out);
            TransformerFactory transFactory = TransformerFactory.newInstance();
            Transformer transformer = transFactory.newTransformer();

            // Important to not hold Configuration log while writing result, since
            // 'out' may be an HDFS stream which needs to lock this configuration
            // from another thread.
            transformer.transform(source, result);
        } catch (TransformerException te) {
            throw new IOException(te);
        }
    }

    /**
     * Return the XML DOM corresponding to this Configuration.
     */
    private synchronized Document asXmlDocument(String propertyName) throws IOException, IllegalArgumentException {
        Document doc;
        try {
            doc = DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();
        } catch (ParserConfigurationException pe) {
            throw new IOException(pe);
        }

        Element conf = doc.createElement("configuration");
        doc.appendChild(conf);
        conf.appendChild(doc.createTextNode("\n"));
        handleDeprecation(); //ensure properties is set and deprecation is handled

        if (!Strings.isNullOrEmpty(propertyName)) {
            if (!properties.containsKey(propertyName)) {
                // given property not found, illegal argument
                throw new IllegalArgumentException("Property " + propertyName + " not found");
            } else {
                // given property is found, write single property
                appendXMLProperty(doc, conf, propertyName);
                conf.appendChild(doc.createTextNode("\n"));
            }
        } else {
            // append all elements
            for (Enumeration<Object> e = properties.keys(); e.hasMoreElements();) {
                appendXMLProperty(doc, conf, (String) e.nextElement());
                conf.appendChild(doc.createTextNode("\n"));
            }
        }
        return doc;
    }

    /**
     *  Append a property with its attributes to a given {#link Document}
     *  if the property is found in configuration.
     *
     * @param doc
     * @param conf
     * @param propertyName
     */
    private synchronized void appendXMLProperty(Document doc, Element conf, String propertyName) {
        // skip writing if given property name is empty or null
        if (!Strings.isNullOrEmpty(propertyName)) {
            String value = properties.getProperty(propertyName);
            if (value != null) {
                Element propNode = doc.createElement("property");
                conf.appendChild(propNode);

                Element nameNode = doc.createElement("name");
                nameNode.appendChild(doc.createTextNode(propertyName));
                propNode.appendChild(nameNode);

                Element valueNode = doc.createElement("value");
                valueNode.appendChild(doc.createTextNode(properties.getProperty(propertyName)));
                propNode.appendChild(valueNode);

                Element finalNode = doc.createElement("final");
                finalNode.appendChild(doc.createTextNode(String.valueOf(finalParameters.contains(propertyName))));
                propNode.appendChild(finalNode);

                if (updatingResource != null) {
                    String[] sources = updatingResource.get(propertyName);
                    if (sources != null) {
                        for (String s : sources) {
                            Element sourceNode = doc.createElement("source");
                            sourceNode.appendChild(doc.createTextNode(s));
                            propNode.appendChild(sourceNode);
                        }
                    }
                }
            }
        }
    }

    /**
     *  Writes properties and their attributes (final and resource)
     *  to the given {@link Writer}.
     *
     *  <li>
     *  When propertyName is not empty, and the property exists
     *  in the configuration, the format of the output would be,
     *  <pre>
     *  {
     *    "property": {
     *      "key" : "key1",
     *      "value" : "value1",
     *      "isFinal" : "key1.isFinal",
     *      "resource" : "key1.resource"
     *    }
     *  }
     *  </pre>
     *  </li>
     *
     *  <li>
     *  When propertyName is null or empty, it behaves same as
     *  {@link #dumpConfiguration(Configuration, Writer)}, the
     *  output would be,
     *  <pre>
     *  { "properties" :
     *      [ { key : "key1",
     *          value : "value1",
     *          isFinal : "key1.isFinal",
     *          resource : "key1.resource" },
     *        { key : "key2",
     *          value : "value2",
     *          isFinal : "ke2.isFinal",
     *          resource : "key2.resource" }
     *       ]
     *   }
     *  </pre>
     *  </li>
     *
     *  <li>
     *  When propertyName is not empty, and the property is not
     *  found in the configuration, this method will throw an
     *  {@link IllegalArgumentException}.
     *  </li>
     *  <p>
     * @param config the configuration
     * @param propertyName property name
     * @param out the Writer to write to
     * @throws IOException
     * @throws IllegalArgumentException when property name is not
     *   empty and the property is not found in configuration
     **/
    public static void dumpConfiguration(Configuration config, String propertyName, Writer out) throws IOException {
        if (Strings.isNullOrEmpty(propertyName)) {
            dumpConfiguration(config, out);
        } else if (Strings.isNullOrEmpty(config.get(propertyName))) {
            throw new IllegalArgumentException("Property " + propertyName + " not found");
        } else {
            JsonFactory dumpFactory = new JsonFactory();
            JsonGenerator dumpGenerator = dumpFactory.createGenerator(out);
            dumpGenerator.writeStartObject();
            dumpGenerator.writeFieldName("property");
            appendJSONProperty(dumpGenerator, config, propertyName, new ConfigRedactor(config));
            dumpGenerator.writeEndObject();
            dumpGenerator.flush();
        }
    }

    /**
     *  Writes out all properties and their attributes (final and resource) to
     *  the given {@link Writer}, the format of the output would be,
     *
     *  <pre>
     *  { "properties" :
     *      [ { key : "key1",
     *          value : "value1",
     *          isFinal : "key1.isFinal",
     *          resource : "key1.resource" },
     *        { key : "key2",
     *          value : "value2",
     *          isFinal : "ke2.isFinal",
     *          resource : "key2.resource" }
     *       ]
     *   }
     *  </pre>
     *
     *  It does not output the properties of the configuration object which
     *  is loaded from an input stream.
     *  <p>
     *
     * @param config the configuration
     * @param out the Writer to write to
     * @throws IOException
     */
    public static void dumpConfiguration(Configuration config, Writer out) throws IOException {
        JsonFactory dumpFactory = new JsonFactory();
        JsonGenerator dumpGenerator = dumpFactory.createGenerator(out);
        dumpGenerator.writeStartObject();
        dumpGenerator.writeFieldName("properties");
        dumpGenerator.writeStartArray();
        dumpGenerator.flush();
        ConfigRedactor redactor = new ConfigRedactor(config);
        synchronized (config) {
            for (Map.Entry<Object, Object> item : config.getProps().entrySet()) {
                appendJSONProperty(dumpGenerator, config, item.getKey().toString(), redactor);
            }
        }
        dumpGenerator.writeEndArray();
        dumpGenerator.writeEndObject();
        dumpGenerator.flush();
    }

    /**
     * Write property and its attributes as json format to given
     * {@link JsonGenerator}.
     *
     * @param jsonGen json writer
     * @param config configuration
     * @param name property name
     * @throws IOException
     */
    private static void appendJSONProperty(JsonGenerator jsonGen, Configuration config, String name,
            ConfigRedactor redactor) throws IOException {
        // skip writing if given property name is empty or null
        if (!Strings.isNullOrEmpty(name) && jsonGen != null) {
            jsonGen.writeStartObject();
            jsonGen.writeStringField("key", name);
            jsonGen.writeStringField("value", redactor.redact(name, config.get(name)));
            jsonGen.writeBooleanField("isFinal", config.finalParameters.contains(name));
            String[] resources = config.updatingResource != null ? config.updatingResource.get(name) : null;
            String resource = UNKNOWN_RESOURCE;
            if (resources != null && resources.length > 0) {
                resource = resources[0];
            }
            jsonGen.writeStringField("resource", resource);
            jsonGen.writeEndObject();
        }
    }

    /**
     * Get the {@link ClassLoader} for this job.
     *
     * @return the correct class loader.
     */
    public ClassLoader getClassLoader() {
        return classLoader;
    }

    /**
     * Set the class loader that will be used to load the various objects.
     * 
     * @param classLoader the new class loader.
     */
    public void setClassLoader(ClassLoader classLoader) {
        this.classLoader = classLoader;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("Configuration: ");
        if (loadDefaults) {
            toString(defaultResources, sb);
            if (resources.size() > 0) {
                sb.append(", ");
            }
        }
        toString(resources, sb);
        return sb.toString();
    }

    private <T> void toString(List<T> resources, StringBuilder sb) {
        ListIterator<T> i = resources.listIterator();
        while (i.hasNext()) {
            if (i.nextIndex() != 0) {
                sb.append(", ");
            }
            sb.append(i.next());
        }
    }

    /** 
     * Set the quietness-mode. 
     * 
     * In the quiet-mode, error and informational messages might not be logged.
     * 
     * @param quietmode <code>true</code> to set quiet-mode on, <code>false</code>
     *              to turn it off.
     */
    public synchronized void setQuietMode(boolean quietmode) {
        this.quietmode = quietmode;
    }

    synchronized boolean getQuietMode() {
        return this.quietmode;
    }

    /** For debugging.  List non-default properties to the terminal and exit. */
    public static void main(String[] args) throws Exception {
        new Configuration().writeXml(System.out);
    }

    @Override
    public void readFields(DataInput in) throws IOException {
        clear();
        int size = WritableUtils.readVInt(in);
        for (int i = 0; i < size; ++i) {
            String key = org.apache.hadoop.io.Text.readString(in);
            String value = org.apache.hadoop.io.Text.readString(in);
            set(key, value);
            String sources[] = WritableUtils.readCompressedStringArray(in);
            if (sources != null) {
                putIntoUpdatingResource(key, sources);
            }
        }
    }

    //@Override
    @Override
    public void write(DataOutput out) throws IOException {
        Properties props = getProps();
        WritableUtils.writeVInt(out, props.size());
        for (Map.Entry<Object, Object> item : props.entrySet()) {
            org.apache.hadoop.io.Text.writeString(out, (String) item.getKey());
            org.apache.hadoop.io.Text.writeString(out, (String) item.getValue());
            WritableUtils.writeCompressedStringArray(out,
                    updatingResource != null ? updatingResource.get(item.getKey()) : null);
        }
    }

    /**
     * get keys matching the the regex 
     * @param regex
     * @return Map<String,String> with matching keys
     */
    public Map<String, String> getValByRegex(String regex) {
        Pattern p = Pattern.compile(regex);

        Map<String, String> result = new HashMap<String, String>();
        Matcher m;

        for (Map.Entry<Object, Object> item : getProps().entrySet()) {
            if (item.getKey() instanceof String && item.getValue() instanceof String) {
                m = p.matcher((String) item.getKey());
                if (m.find()) { // match
                    result.put((String) item.getKey(),
                            substituteVars(getProps().getProperty((String) item.getKey())));
                }
            }
        }
        return result;
    }

    /**
     * A unique class which is used as a sentinel value in the caching
     * for getClassByName. {@link Configuration#getClassByNameOrNull(String)}
     */
    private static abstract class NegativeCacheSentinel {
    }

    public static void dumpDeprecatedKeys() {
        DeprecationContext deprecations = deprecationContext.get();
        for (Map.Entry<String, DeprecatedKeyInfo> entry : deprecations.getDeprecatedKeyMap().entrySet()) {
            StringBuilder newKeys = new StringBuilder();
            for (String newKey : entry.getValue().newKeys) {
                newKeys.append(newKey).append("\t");
            }
            System.out.println(entry.getKey() + "\t" + newKeys.toString());
        }
    }

    /**
     * Returns whether or not a deprecated name has been warned. If the name is not
     * deprecated then always return false
     */
    public static boolean hasWarnedDeprecation(String name) {
        DeprecationContext deprecations = deprecationContext.get();
        if (deprecations.getDeprecatedKeyMap().containsKey(name)) {
            if (deprecations.getDeprecatedKeyMap().get(name).accessed.get()) {
                return true;
            }
        }
        return false;
    }

    /**
     * Get all properties belonging to tag.
     * @param tag tag
     * @return Properties with matching tag
     */
    public Properties getAllPropertiesByTag(final String tag) {
        Properties props = new Properties();
        if (propertyTagsMap.containsKey(tag)) {
            props.putAll(propertyTagsMap.get(tag));
        }
        return props;
    }

    /**
     * Get all properties belonging to list of input tags. Calls
     * getAllPropertiesByTag internally.
     * @param tagList list of input tags
     * @return Properties with matching tags
     */
    public Properties getAllPropertiesByTags(final List<String> tagList) {
        Properties prop = new Properties();
        for (String tag : tagList) {
            prop.putAll(this.getAllPropertiesByTag(tag));
        }
        return prop;
    }

    /**
     * Get Property tag Enum corresponding to given source.
     *
     * @param tagStr String representation of Enum
     * @return true if tagStr is a valid tag
     */
    public boolean isPropertyTag(String tagStr) {
        return this.TAGS.contains(tagStr);
    }

    private void putIntoUpdatingResource(String key, String[] value) {
        Map<String, String[]> localUR = updatingResource;
        if (localUR == null) {
            synchronized (this) {
                localUR = updatingResource;
                if (localUR == null) {
                    updatingResource = localUR = new ConcurrentHashMap<>(8);
                }
            }
        }
        localUR.put(key, value);
    }
}