Java tutorial
/* * Copyright 2001-2004 The Apache Software Foundation. * * Licensed 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.commons.logging.impl; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogConfigurationException; import org.apache.commons.logging.LogFactory; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.slf4j.spi.LocationAwareLogger; import java.util.ArrayList; import java.util.Enumeration; import java.util.Hashtable; import java.util.List; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.ConcurrentMap; /** * <p> * Concrete subclass of {@link LogFactory} which always delegates to the * {@link LoggerFactory org.slf4j.LoggerFactory} class. * * <p> * This factory generates instances of {@link SLF4JLog}. It will remember * previously created instances for the same name, and will return them on * repeated requests to the <code>getInstance()</code> method. * * <p> * This implementation ignores any configured attributes. * </p> * * @author Rod Waldhoff * @author Craig R. McClanahan * @author Richard A. Sitze * @author Ceki Gülcü */ @SuppressWarnings("rawtypes") public class SLF4JLogFactory extends LogFactory { // ----------------------------------------------------------- Constructors /** * The {@link org.apache.commons.logging.Log}instances that have already been * created, keyed by logger name. */ ConcurrentMap<String, Log> loggerMap; /** * Public no-arguments constructor required by the lookup mechanism. */ public SLF4JLogFactory() { loggerMap = new ConcurrentHashMap<String, Log>(); } // ----------------------------------------------------- Manifest Constants /** * The name of the system property identifying our {@link Log}implementation * class. */ public static final String LOG_PROPERTY = "org.apache.commons.logging.Log"; // ----------------------------------------------------- Instance Variables /** * Configuration attributes. */ protected Hashtable attributes = new Hashtable(); // --------------------------------------------------------- Public Methods /** * Return the configuration attribute with the specified name (if any), or * <code>null</code> if there is no such attribute. * * @param name * Name of the attribute to return */ public Object getAttribute(String name) { return (attributes.get(name)); } /** * Return an array containing the names of all currently defined configuration * attributes. If there are no such attributes, a zero length array is * returned. */ @SuppressWarnings("unchecked") public String[] getAttributeNames() { List<String> names = new ArrayList<String>(); Enumeration<String> keys = attributes.keys(); while (keys.hasMoreElements()) { names.add((String) keys.nextElement()); } String results[] = new String[names.size()]; for (int i = 0; i < results.length; i++) { results[i] = (String) names.get(i); } return (results); } /** * Convenience method to derive a name from the specified class and call * <code>getInstance(String)</code> with it. * * @param clazz * Class for which a suitable Log name will be derived * * @exception LogConfigurationException * if a suitable <code>Log</code> instance cannot be returned */ public Log getInstance(Class clazz) throws LogConfigurationException { return (getInstance(clazz.getName())); } /** * <p> * Construct (if necessary) and return a <code>Log</code> instance, using * the factory's current set of configuration attributes. * </p> * * @param name * Logical name of the <code>Log</code> instance to be returned * (the meaning of this name is only known to the underlying logging * implementation that is being wrapped) * * @exception LogConfigurationException * if a suitable <code>Log</code> instance cannot be returned */ public Log getInstance(String name) throws LogConfigurationException { Log instance = loggerMap.get(name); if (instance != null) { return instance; } else { Log newInstance; Logger slf4jLogger = LoggerFactory.getLogger(name); if (slf4jLogger instanceof LocationAwareLogger) { newInstance = new SLF4JLocationAwareLog((LocationAwareLogger) slf4jLogger); } else { newInstance = new SLF4JLog(slf4jLogger); } Log oldInstance = loggerMap.putIfAbsent(name, newInstance); return oldInstance == null ? newInstance : oldInstance; } } /** * Release any internal references to previously created * {@link org.apache.commons.logging.Log}instances returned by this factory. * This is useful in environments like servlet containers, which implement * application reloading by throwing away a ClassLoader. Dangling references * to objects in that class loader would prevent garbage collection. */ public void release() { // This method is never called by jcl-over-slf4j classes. However, // in certain deployment scenarios, in particular if jcl-over-slf4j.jar // is // in the the web-app class loader and the official commons-logging.jar is // deployed in some parent class loader (e.g. commons/lib), then it is // possible // for the parent class loader to mask the classes shipping in // jcl-over-slf4j.jar. System.out.println("WARN: The method " + SLF4JLogFactory.class + "#release() was invoked."); System.out.println("WARN: Please see http://www.slf4j.org/codes.html#release for an explanation."); System.out.flush(); } /** * Remove any configuration attribute associated with the specified name. If * there is no such attribute, no action is taken. * * @param name * Name of the attribute to remove */ public void removeAttribute(String name) { attributes.remove(name); } /** * Set the configuration attribute with the specified name. Calling this with * a <code>null</code> value is equivalent to calling * <code>removeAttribute(name)</code>. * * @param name * Name of the attribute to set * @param value * Value of the attribute to set, or <code>null</code> to remove * any setting for this attribute */ @SuppressWarnings("unchecked") public void setAttribute(String name, Object value) { if (value == null) { attributes.remove(name); } else { attributes.put(name, value); } } }