Java tutorial
/** * 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.atlas; import org.apache.atlas.security.InMemoryJAASConfiguration; import org.apache.commons.configuration.Configuration; import org.apache.commons.configuration.ConfigurationException; import org.apache.commons.configuration.PropertiesConfiguration; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.InputStream; import java.net.URL; import java.util.Iterator; /** * Application properties used by Atlas. */ public final class ApplicationProperties extends PropertiesConfiguration { public static final String ATLAS_CONFIGURATION_DIRECTORY_PROPERTY = "atlas.conf"; private static final Logger LOG = LoggerFactory.getLogger(ApplicationProperties.class); public static final String APPLICATION_PROPERTIES = "atlas-application.properties"; private static volatile Configuration instance = null; private ApplicationProperties(URL url) throws ConfigurationException { super(url); } public static void forceReload() { if (instance != null) { synchronized (ApplicationProperties.class) { if (instance != null) { instance = null; } } } } public static Configuration get() throws AtlasException { if (instance == null) { synchronized (ApplicationProperties.class) { if (instance == null) { instance = get(APPLICATION_PROPERTIES); InMemoryJAASConfiguration.init(instance); } } } return instance; } public static Configuration get(String fileName) throws AtlasException { String confLocation = System.getProperty(ATLAS_CONFIGURATION_DIRECTORY_PROPERTY); try { URL url = null; if (confLocation == null) { LOG.info("Looking for {} in classpath", fileName); url = ApplicationProperties.class.getClassLoader().getResource(fileName); if (url == null) { LOG.info("Looking for /{} in classpath", fileName); url = ApplicationProperties.class.getClassLoader().getResource("/" + fileName); } } else { url = new File(confLocation, fileName).toURI().toURL(); } LOG.info("Loading {} from {}", fileName, url); Configuration configuration = new ApplicationProperties(url).interpolatedConfiguration(); logConfiguration(configuration); return configuration; } catch (Exception e) { throw new AtlasException("Failed to load application properties", e); } } private static void logConfiguration(Configuration configuration) { if (LOG.isDebugEnabled()) { Iterator<String> keys = configuration.getKeys(); LOG.debug("Configuration loaded:"); while (keys.hasNext()) { String key = keys.next(); LOG.debug("{} = {}", key, configuration.getProperty(key)); } } } public static Configuration getSubsetConfiguration(Configuration inConf, String prefix) { return inConf.subset(prefix); } public static Class getClass(Configuration configuration, String propertyName, String defaultValue, Class assignableClass) throws AtlasException { try { String propertyValue = configuration.getString(propertyName, defaultValue); Class<?> clazz = Class.forName(propertyValue); if (assignableClass == null || assignableClass.isAssignableFrom(clazz)) { return clazz; } else { String message = "Class " + clazz.getName() + " specified in property " + propertyName + " is not assignable to class " + assignableClass.getName(); LOG.error(message); throw new AtlasException(message); } } catch (Exception e) { throw new AtlasException(e); } } /** * Get the specified property as an {@link InputStream}. * If the property is not set, then the specified default filename * is searched for in the following locations, in order of precedence: * 1. Atlas configuration directory specified by the {@link #ATLAS_CONFIGURATION_DIRECTORY_PROPERTY} system property * 2. relative to the working directory if {@link #ATLAS_CONFIGURATION_DIRECTORY_PROPERTY} is not set * 3. as a classloader resource * * @param configuration * @param propertyName * @param defaultFileName name of file to use by default if specified property is not set in the configuration- if null, * an {@link AtlasException} is thrown if the property is not set * @return an {@link InputStream} * @throws AtlasException if no file was found or if there was an error loading the file */ public static InputStream getFileAsInputStream(Configuration configuration, String propertyName, String defaultFileName) throws AtlasException { File fileToLoad = null; String fileName = configuration.getString(propertyName); if (fileName == null) { if (defaultFileName == null) { throw new AtlasException(propertyName + " property not set and no default value specified"); } fileName = defaultFileName; String atlasConfDir = System.getProperty(ATLAS_CONFIGURATION_DIRECTORY_PROPERTY); if (atlasConfDir != null) { // Look for default filename in Atlas config directory fileToLoad = new File(atlasConfDir, fileName); } else { // Look for default filename under the working directory fileToLoad = new File(fileName); } if (LOG.isDebugEnabled()) { LOG.debug("{} property not set - defaulting to {}", propertyName, fileToLoad.getPath()); } } else { // Look for configured filename fileToLoad = new File(fileName); if (LOG.isDebugEnabled()) { LOG.debug("Using {} property setting: {}", propertyName, fileToLoad.getPath()); } } InputStream inStr = null; if (fileToLoad.exists()) { try { inStr = new FileInputStream(fileToLoad); } catch (FileNotFoundException e) { throw new AtlasException("Error loading file " + fileName, e); } if (LOG.isDebugEnabled()) { LOG.debug("Loaded file from : {}", fileToLoad.getPath()); } } else { // Look for file as class loader resource inStr = Thread.currentThread().getContextClassLoader().getResourceAsStream(fileName); if (inStr == null) { String msg = fileName + " not found in file system or as class loader resource"; LOG.error(msg); throw new AtlasException(msg); } if (LOG.isDebugEnabled()) { LOG.debug("Loaded {} as resource from : {}", fileName, Thread.currentThread().getContextClassLoader().getResource(fileName).toString()); } } return inStr; } }