/* * 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 java.lang.reflect.Constructor;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.security.AccessController;import java.security.PrivilegedAction;import java.util.Enumeration;import java.util.Hashtable;import java.util.Vector;import org.apache.commons.logging.Log;import org.apache.commons.logging.LogConfigurationException;import org.apache.commons.logging.LogFactory;/** * <p>Concrete subclass of {@link LogFactory} that implements the * following algorithm to dynamically select a logging implementation * class to instantiate a wrapper for.</p> * <ul> * <li>Use a factory configuration attribute named *     <code>org.apache.commons.logging.Log</code> to identify the *     requested implementation class.</li> * <li>Use the <code>org.apache.commons.logging.Log</code> system property *     to identify the requested implementation class.</li> * <li>If <em>Log4J</em> is available, return an instance of *     <code>org.apache.commons.logging.impl.Log4JLogger</code>.</li> * <li>If <em>JDK 1.4 or later</em> is available, return an instance of *     <code>org.apache.commons.logging.impl.Jdk14Logger</code>.</li> * <li>Otherwise, return an instance of *     <code>org.apache.commons.logging.impl.SimpleLog</code>.</li> * </ul> * * <p>If the selected {@link Log} implementation class has a * <code>setLogFactory()</code> method that accepts a {@link LogFactory} * parameter, this method will be called on each newly created instance * to identify the associated factory.  This makes factory configuration * attributes available to the Log instance, if it so desires.</p> * * <p>This factory will remember previously created <code>Log</code> instances * for the same name, and will return them on repeated requests to the * <code>getInstance()</code> method.  This implementation ignores any * configured attributes.</p> * * @author Rod Waldhoff * @author Craig R. McClanahan * @author Richard A. Sitze * @version $Revision: 1.33 $ $Date: 2004/03/06 21:52:59 $ */public class LogFactoryImpl extends LogFactory {    // ----------------------------------------------------------- Constructors    /**     * Public no-arguments constructor required by the lookup mechanism.     */    public LogFactoryImpl() {        super();    }    // ----------------------------------------------------- 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";    /**     * The deprecated system property used for backwards compatibility with     * the old {@link org.apache.commons.logging.LogSource} class.     */    protected static final String LOG_PROPERTY_OLD =        "org.apache.commons.logging.log";    /**     * <p>The name of the {@link Log} interface class.</p>     */    private static final String LOG_INTERFACE =        "org.apache.commons.logging.Log";    // ----------------------------------------------------- Instance Variables    /**     * Configuration attributes.     */    protected Hashtable attributes = new Hashtable();    /**     * The {@link org.apache.commons.logging.Log} instances that have     * already been created, keyed by logger name.     */    protected Hashtable instances = new Hashtable();    /**     * Name of the class implementing the Log interface.     */    private String logClassName;    /**     * The one-argument constructor of the     * {@link org.apache.commons.logging.Log}     * implementation class that will be used to create new instances.     * This value is initialized by <code>getLogConstructor()</code>,     * and then returned repeatedly.     */    protected Constructor logConstructor = null;    /**     * The signature of the Constructor to be used.     */    protected Class logConstructorSignature[] =    { java.lang.String.class };    /**     * The one-argument <code>setLogFactory</code> method of the selected     * {@link org.apache.commons.logging.Log} method, if it exists.     */    protected Method logMethod = null;    /**     * The signature of the <code>setLogFactory</code> method to be used.     */    protected Class logMethodSignature[] =    { LogFactory.class };    // --------------------------------------------------------- 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.     */    public String[] getAttributeNames() {        Vector names = new Vector();        Enumeration keys = attributes.keys();        while (keys.hasMoreElements()) {            names.addElement((String) keys.nextElement());        }        String results[] = new String[names.size()];        for (int i = 0; i < results.length; i++) {            results[i] = (String) names.elementAt(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>     *     * <p><strong>NOTE</strong> - Depending upon the implementation of     * the <code>LogFactory</code> you are using, the <code>Log</code>     * instance you are returned may or may not be local to the current     * application, and may or may not be returned again on a subsequent     * call with the same name argument.</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 = (Log) instances.get(name);        if (instance == null) {            instance = newInstance(name);            instances.put(name, instance);        }        return (instance);    }    /**     * 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() {        instances.clear();    }    /**     * 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