private static void init() {
		if (factory != null) {
			return;
		}
		
		/*
		 *使用log4j，
		 *如果没有则用基于|Java.util.logging.Logger|实现的|JdkLogger| 和|JdkLoggerFactory|
		 */
		try {
			Class.forName("org.apache.log4j.Logger");
			Class<?> log4jLoggerFactory = Class.forName("com.jfinal.log.Log4jLoggerFactory");
			factory = (ILoggerFactory) log4jLoggerFactory.newInstance();
		} catch (Exception e) {
			factory = new JdkLoggerFactory();
		}
	}