JMX : Notification

JMX API 定义了一种机制，使得MBean可以产生notification，以在状态变化时、特定事件发生时或者出问题时，发出一个提醒。

state change, a detected event, a problem

generate notification : MBean必须implement NotificationEmitter或extend NotificationBroadcasterSupport。

send notification : 创建javax.management.Notification或者其子类，并调用NotificationBroadcasterSupport.sendNotification()

source:

每个notification都会有个源(source)，就是相应的ObjectName。

sequence number:

每个notification都会有个sequence number。用于给来自同一个source的notification编号。

当处理notification的顺序有影响的时候，sequence number就派上用场了。

可以是0，但最好不要是一个source每生成一个notification时，就增加一下。

示例:

package test.xue.mbean;

import javax.management.AttributeChangeNotification;
import javax.management.Notification;
import javax.management.NotificationBroadcasterSupport;

public class Hello extends NotificationBroadcasterSupport implements HelloMBean {

	private final String name = "My HelloMBean";
	private int cacheSize = 1024;
	private String title;

	private long sequenceNo = 1;

	@Override
	public void sayHello() {
		System.out.println("hello, my HelloMBean");
	}

	@Override
	public int add(int x, int y) {
		return x + y;
	}

	@Override
	public String getName() {
		return name;
	}

	@Override
	public int getCacheSize() {
		return cacheSize;
	}

	@Override
	public synchronized void setCacheSize(int size) {
		int oldSize = this.cacheSize;
		this.cacheSize = size;
		System.out.println("cacheSize changed : " + size);

		Notification notification = new AttributeChangeNotification(this, sequenceNo++,
				System.currentTimeMillis(), "cacheSize changed", "cacheSize",
				"int", oldSize, this.cacheSize);
		
		sendNotification(notification);
	}
	
	@Override
	public void setText() {
		System.out.println("setText called");
	}

	@Override
	public void settitle(String title) {
		this.title = title;
		System.out.println("title changed : " + title);
	}
}

与前面的Standard MBean没什么区别，只是继承了 NotificationBroadcasterSupport类，并且在setCacheSize的时候，生成并发送了notification。

JConsole测试:

点击“订阅”，以后才能接收到source发出的notification。

修改了属性CacheSize后，JConsole会接到通知。