java Thread start() 特性

写了两个简单的类。本来写这两个类的初衷是为了 验证 log4j 异步打印日志时的 MDC 衔接问题。但是由于疏忽，有个地方写错了。

public class TestLog {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		for (int i = 1; i <= 5; i++) {
			LogThread lt = new LogThread("aaa_" + i);
			lt.setName("aaa_" + i);
			lt.start();
		}
	}

}

 

public class LogThread extends Thread{
	String message;
	private Logger log = Logger.getLogger(this.getClass().getName());
	public LogThread(String tranId) { 
		this.message =  tranId;
		MDC.put("tranId", message);
	}
	@Override
	public void run() {
			log.info(message+"_"+MDC.get("tranId"));
	}
}

 运行结果如下：

[105614.713][INFO ](aaa_1) aaa_1_null  [LogThread.java:18 ]
[105614.713][INFO ](aaa_4) aaa_4_aaa_3  [LogThread.java:18 ]
[105614.713][INFO ](aaa_3) aaa_3_aaa_2  [LogThread.java:18 ]
[105614.713][INFO ](aaa_2) aaa_2_aaa_1  [LogThread.java:18 ]
[105614.713][INFO ](aaa_5) aaa_5_aaa_4  [LogThread.java:18 ]

能看出什么地方写错了吗？