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The free Java library for Asterisk PBX integration.
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/*
 *  Copyright 2004-2006 Stefan Reuter
 *
 *  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.asteriskjava.util;

import org.asteriskjava.util.internal.JavaLoggingLog;
import org.asteriskjava.util.internal.Log4JLogger;
import org.asteriskjava.util.internal.NullLog;
import org.asteriskjava.util.internal.Slf4JLogger;

/**
 * Facade to hide details of the underlying logging system.
 * 
 * If you want to reuse Asterisk-Java's logging abstraction layer add a private
 * attribute to your class like this:
 *
 * 
 * private final Log logger = LogFactory.getLog(getClass());
 * 
 * 
 * and then use the methods defined in {@link org.asteriskjava.util.Log}:
 *
 * 
 * logger.error("Unable to create new instance of " + eventClass, ex);
 * 
 * 
 * Asterisk-Java's logging abstraction layer uses log4j when available and falls
 * back to java.util.logging otherwise.
 *
 * @author srt
 * @version $Id$
 */
public final class LogFactory {
    private static Boolean slf4jLoggingAvailable = null;

    /**
     * Indicates if log4j is available on the classpath or not. If the check has
     * not yet performed this is null.
     */
    private static Boolean log4jLoggingAvailable = null;

    /**
     * Indicates if java.util.logging is available on the classpath or not. If
     * the check has not yet performed this is null.
     */
    private static Boolean javaLoggingAvailable = null;

    private static ClassLoader classLoader = LogFactory.class.getClassLoader();

    private LogFactory() {

    }

    public static void setClassLoader(ClassLoader classLoader) {
        LogFactory.classLoader = classLoader;
    }

    /**
     * Returns an instance of Log suitable for logging from the given class.
     *
     * @param clazz the class to create the logger for.
     * @return the created logger.
     */
    public synchronized static Log getLog(Class clazz) {
        if (slf4jLoggingAvailable == null) {
            try {
                classLoader.loadClass("org.slf4j.Logger");
                slf4jLoggingAvailable = Boolean.TRUE;
            } catch (Exception e) {
                slf4jLoggingAvailable = Boolean.FALSE;
            }
        }

        if (slf4jLoggingAvailable) {
            try {
                return new Slf4JLogger(clazz);
            } catch (Throwable e) {
                slf4jLoggingAvailable = Boolean.FALSE;
            }
        }

        if (log4jLoggingAvailable == null) {
            try {
                classLoader.loadClass("org.apache.logging.log4j.Logger");
                log4jLoggingAvailable = Boolean.TRUE;
            } catch (Exception e) {
                log4jLoggingAvailable = Boolean.FALSE;
            }
        }

        if (log4jLoggingAvailable) {
            return new Log4JLogger(clazz);
        }

        if (javaLoggingAvailable == null) {
            try {
                classLoader.loadClass("java.util.logging.Logger");
                javaLoggingAvailable = Boolean.TRUE;
            } catch (Exception e) {
                javaLoggingAvailable = Boolean.FALSE;
            }
        }
        if (javaLoggingAvailable) {
            return new JavaLoggingLog(clazz);
        }
        return new NullLog();
    }
}