logfactoryimpl.java

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/*
 * 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.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: 1.3 $ $Date: 2004/12/17 15:28:04 $
 */

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);

    }