LoggerFactory.java

// Copyright (c) 2002  SPY internetworking <dustin@spy.net>

package net.spy.log;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

/**
 * Factory to get logger instances.
 * The system property <code>net.spy.log.LoggerImpl</code> should point to
 * an implementation of net.spy.log.Logger to use.
 *
 * <p>
 *  Depending on how and where this was compiled, a sun logger (jdk 1.4)
 *  and/or <a href="http://jakarta.apache.org/log4j/docs/">log4j</a> logger
 *  implementation may be included.  Both are included with the official
 *  distribution.
 * </p>
 *
 * @see AbstractLogger
 */
public final class LoggerFactory extends Object {

	private static LoggerFactory instance=null;

	private final ConcurrentMap<String, Logger> instances;
	private Constructor<? extends Logger> instanceConstructor;

	/**
	 * Get an instance of LoggerFactory.
	 */
	private LoggerFactory() {
		super();

		instances=new ConcurrentHashMap<String, Logger>();
	}

	private static void init() {
        if(instance == null) {
        	instance=new LoggerFactory();
        }
	}

	/**
	 * Get a logger by class.
	 *
	 * @param clazz the class for which we want the logger.
	 * @return a Logger instance
	 */
	public static Logger getLogger(Class<?> clazz) {
		return(getLogger(clazz.getName()));
	}

	/**
	 * Get a logger by name.
	 *
	 * @param name the name for which we want the logger
	 * @return a Logger instance
	 */
	public static Logger getLogger(String name) {
        if(name == null) {
            throw new NullPointerException("Logger name may not be null.");
        }
        init();
        return(instance.internalGetLogger(name));
	}

	// Get an instance of Logger from internal mechanisms.
	private Logger internalGetLogger(String name) {
        assert name != null : "Name was null";
        Logger rv=instances.get(name);

        if (rv==null) {
        	Logger newLogger=null;
			try {
				newLogger=getNewInstance(name);
			} catch(Exception e) {
				throw new RuntimeException("Problem getting logger", e);
			}
            Logger tmp=instances.putIfAbsent(name, newLogger);
            // Return either the new logger we've just made, or one that was
            // created while we were waiting
            rv = tmp == null ? newLogger : tmp;
        }

        return(rv);

	}

	private Logger getNewInstance(String name)
		throws	InstantiationException, IllegalAccessException,
				IllegalArgumentException, InvocationTargetException {

		if(instanceConstructor==null) {
			getConstructor();
		}
		Object[] args={name};
		Logger rv=instanceConstructor.newInstance(args);

		return (rv);
	}

	// Find the appropriate constructor
	@SuppressWarnings("unchecked")
	private void getConstructor() {
		Class<? extends Logger> c=DefaultLogger.class;
		String className=System.getProperty("net.spy.log.LoggerImpl");

		if(className!=null) {
			try {
				c=(Class<? extends Logger>) Class.forName(className);
			} catch(NoClassDefFoundError e) {
				System.err.println("Warning:  " + className
					+ " not found while initializing"
					+ " net.spy.log.LoggerFactory");
				e.printStackTrace();
				c=DefaultLogger.class;
			} catch(ClassNotFoundException e) {
				System.err.println("Warning:  " + className
					+ " not found while initializing"
					+ " net.spy.log.LoggerFactory");
				e.printStackTrace();
				c=DefaultLogger.class;
			}
		}

		// Find the best constructor
		try {
			// Try to find a constructor that takes a single string
			Class[] args={String.class};
			instanceConstructor=c.getConstructor(args);
		} catch(NoSuchMethodException e) {
			try {
				// Try to find an empty constructor
				Class[] args={};
				instanceConstructor=c.getConstructor(args);
			} catch(NoSuchMethodException e2) {
				System.err.println("Warning:  " + className
					+ " has no appropriate constructor, using defaults.");

				// Try to find a constructor that takes a single string
				try {
					Class[] args={String.class};
					instanceConstructor=
						DefaultLogger.class.getConstructor(args);
				} catch(NoSuchMethodException e3) {
					// This shouldn't happen.
					throw new NoSuchMethodError(
						"There used to be a constructor that takes a single "
							+ "String on "
							+ DefaultLogger.class + ", but I can't "
							+ "find one now.");
				} // SOL
			} // No empty constructor
		} // No constructor that takes a string
	} // getConstructor

}