JMX学习笔记

一、什么是JMX

JMX是Java Management Extension的缩写，是Java SE平台的一部分；JMX框架的目的是用来管理我们的Application，设备（比如网络，内存，缓存等）等可以用我们的Java类描述控制的一切“资源”。JMX定义一系列规范（包括命名规范、远程调用协议）、API等，JMX通过Managed Beans（MBeans）来管理制定资源，而这些MBeans都需要注册到一个core-managed object server（MBeans Server） ，该Server可以看成资源管理客户端（或代理），只要可以运行JVM的地方，就可以运行这个代理。

二、JMX框架结构

如下图，应用程序将需要管理的资源类实现MBean的接口（即通过MBean来装配该类），MBean注册到MBeans Server代理；代理通过JMX connector将MBeans接口暴露给客户端（资源监控管理端），客户端就可以通过MBeans接口来实现对Application中的资源进行查询、修改等管理了。其中JMX Connector未指定协议，可以RMI、STMP等协议都可以，只要实现connector接口。

三、实现样例

以Oracle提供JMX样例进行讲解

1）首先定义资源管理类MBean Interface：这个接口定义MBean怎么管理类或资源；按JMX的命名规范，MBean接口必须以MBean结尾。

/*
 * HelloMBean.java - MBean interface describing the management operations and
 * attributes for the Hello World MBean. In this case there are two operations,
 * "sayHello" and "add", and two attributes, "Name" and "CacheSize".
 */

package com.example;

public interface HelloMBean {
    //-----------
    // operations
    //-----------

    public void sayHello();
    public int add(int x, int y);

    //-----------
    // attributes
    //-----------

    // a read-only attribute called Name of type String
    public String getName();

    // a read-write attribute called CacheSize of type int
    public int getCacheSize();
    public void setCacheSize(int size);
}

2）实现MBean 接口。将需要管理的资源，通过接口实现管理。所以在实际开发过程中，可能会先有资源类，后续如果需要对其属性进行管理，再添加MBean接口类和实现方法。

/*
 * Hello.java - MBean implementation for the Hello MBean. This class must
 * implement all the Java methods declared in the HelloMBean interface,
 * with the appropriate behavior for each one.
 */

package com.example;

import javax.management.*;

public class Hello implements HelloMBean {

	public void sayHello() {
		System.out.println("hello, world");
	}

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

	/*
	 * Getter for the Name attribute. The pattern shown here is frequent: the
	 * getter returns a private field representing the attribute value. In our
	 * case, the attribute value never changes, but for other attributes it
	 * might change as the application runs. Consider an attribute representing
	 * statistics such as uptime or memory usage, for example. Being read-only
	 * just means that it can't be changed through the management interface.
	 */
	public String getName() {
		return this.name;
	}

	/*
	 * Getter for the CacheSize attribute. The pattern shown here is frequent:
	 * the getter returns a private field representing the attribute value, and
	 * the setter changes that field.
	 */
	public int getCacheSize() {
		return this.cacheSize;
	}

	/*
	 * Setter for the CacheSize attribute. To avoid problems with stale values
	 * in multithreaded situations, it is a good idea for setters to be
	 * synchronized.
	 */
	public synchronized void setCacheSize(int size) {
		int oldSize = this.cacheSize;
		this.cacheSize = size;

		/*
		 * In a real application, changing the attribute would typically have
		 * effects beyond just modifying the cacheSize field. For example,
		 * resizing the cache might mean discarding entries or allocating new
		 * ones. The logic for these effects would be here.
		 */
		System.out.println("Cache size now " + this.cacheSize);
	}

	private final String name = "Reginald";
	private int cacheSize = DEFAULT_CACHE_SIZE;
	private static final int DEFAULT_CACHE_SIZE = 200;

	private long sequenceNumber = 1;
}

3）创建MBeans的代理，并将实现的MBean注册到代理，以便远程客户端可以访问。

/*
 * Main.java - main class for the Hello MBean and QueueSampler MXBean example.
 * Create the Hello MBean and QueueSampler MXBean, register them in the platform
 * MBean server, then wait forever (or until the program is interrupted).
 */

package com.example;

import java.lang.management.ManagementFactory;
import java.util.Queue;
import java.util.concurrent.ArrayBlockingQueue;
import javax.management.MBeanServer;
import javax.management.ObjectName;

public class Main {
	/*
	 * For simplicity, we declare "throws Exception". Real programs will usually
	 * want finer-grained exception handling.
	 */
	public static void main(String[] args) throws Exception {
		// Get the Platform MBean Server
		MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();

		// Construct the ObjectName for the Hello MBean we will register
		ObjectName mbeanName = new ObjectName("com.example:type=Hello");

		// Create the Hello World MBean
		Hello mbean = new Hello();

		// Register the Hello World MBean
		mbs.registerMBean(mbean, mbeanName);

		// Wait forever
		System.out.println("Waiting for incoming requests...");
		Thread.sleep(Long.MAX_VALUE);
	}
}

4）启动本地服务,执行com.example.Main.main()方法，进行验证。其中客户端，可以启用Oracle JDK带的Jconsole连接本地的代理。