Java example source code file (SLF4JLogFactory.java)

This example Java source code file (SLF4JLogFactory.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

arraylist, concurrenthashmap, enumeration, hashtable, locationawarelogger, log, log_property, logconfigurationexception, logger, object, slf4jlocationawarelog, slf4jlogfactory, string, suppresswarnings, threading, threads, util

The SLF4JLogFactory.java Java example source code

/*
 * 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() 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 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();
        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) with it.
     * 
     * @param clazz
     *          Class for which a suitable Log name will be derived
     * 
     * @exception LogConfigurationException
     *              if a suitable <code>Log instance cannot be returned
     */
    public Log getInstance(Class clazz) throws LogConfigurationException {
        return (getInstance(clazz.getName()));
    }

    /**
     * <p>
     * Construct (if necessary) and return a <code>Log instance, using
     * the factory's current set of configuration attributes.
     * </p>
     * 
     * @param name
     *          Logical name of the <code>Log 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 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 value is equivalent to calling
     * <code>removeAttribute(name).
     * 
     * @param name
     *          Name of the attribute to set
     * @param value
     *          Value of the attribute to set, or <code>null 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);
        }

    }
}