JMX（四）DynamicMBean

动态MBean是在运行期才定义它的属性和方法，也就是说它有什么属性和方法是可以动态改变的。动态MBean主要利用一些辅助类（构造函数类MBeanConstructorInfo、属性类MBeanAttributeInfo、方法类MBeanOperationInfo）来完成这个功能，所有的动态MBean必须实现DynamicMBean接口。DynamicMBean写好后，使用方法和第一篇文章中普通的MBean一样。

给出一个动态MBean的实例，这个实例最初动态构了一个Name属性及一个print方法，当我们执行它的print方法之后，又给此MBean新增了一个print1方法。实例的代码如下： 

 

1.HelloDynamic

package jmx.dynamicmbean;

import java.lang.reflect.Constructor;
import java.util.Iterator;
import javax.management.Attribute;
import javax.management.AttributeList;
import javax.management.DynamicMBean;
import javax.management.MBeanAttributeInfo;
import javax.management.MBeanConstructorInfo;
import javax.management.MBeanException;
import javax.management.MBeanInfo;
import javax.management.MBeanNotificationInfo;
import javax.management.MBeanOperationInfo;
import javax.management.MBeanParameterInfo;
import javax.management.ReflectionException;
/**
 * 动态MBean主要利用一些辅助类（构造函数类MBeanConstructorInfo、属性类MBeanAttributeInfo、方法类MBeanOperationInfo）
 * 来完成这个功能，所有的动态MBean必须实现DynamicMBean接口
 * @author chenyw
 *
 */
public class HelloDynamic implements DynamicMBean {
	// 这是我们的属性名称
	private String name;
	private MBeanInfo mBeanInfo = null;
	private String className;
	private String description;
	private MBeanAttributeInfo[] attributes;
	private MBeanConstructorInfo[] constructors;
	private MBeanOperationInfo[] operations;
	MBeanNotificationInfo[] mBeanNotificationInfoArray;

	public HelloDynamic() {
		init();
		buildDynamicMBean();
	}

	private void init() {
		className = this.getClass().getName();
		description = "Simple implementation of a dynamic MBean.";
		attributes = new MBeanAttributeInfo[1];
		constructors = new MBeanConstructorInfo[1];
		operations = new MBeanOperationInfo[1];
		mBeanNotificationInfoArray = new MBeanNotificationInfo[0];
	}

	private void buildDynamicMBean() {
		// 设定构造函数
		Constructor[] thisconstructors = this.getClass().getConstructors();
		constructors[0] = new MBeanConstructorInfo(
				"HelloDynamic(): Constructs a HelloDynamic object",
				thisconstructors[0]);
		// 设定一个属性
		attributes[0] = new MBeanAttributeInfo("Name", "java.lang.String",
				"Name: name string.", true, true, false);
		// operate method 我们的操作方法是print
		MBeanParameterInfo[] params = null;// 无参数
		operations[0] = new MBeanOperationInfo("print",
				"print(): print the name", params, "void",
				MBeanOperationInfo.INFO);
		mBeanInfo = new MBeanInfo(className, description, attributes,
				constructors, operations, mBeanNotificationInfoArray);
	} // 动态增加一个print1方法

	private void dynamicAddOperation() {
		init();
		operations = new MBeanOperationInfo[2];// 设定数组为两个
		buildDynamicMBean();
		operations[1] = new MBeanOperationInfo("print1",
				"print1(): print the name", null, "void",
				MBeanOperationInfo.INFO);
		mBeanInfo = new MBeanInfo(className, description, attributes,
				constructors, operations, mBeanNotificationInfoArray);
	}

	public Object getAttribute(String attribute_name) {
		if (attribute_name != null)
			return null;
		if (attribute_name.equals("Name"))
			return name;
		return null;
	}

	public void setAttribute(Attribute attribute) {
		if (attribute == null)
			return;
		String Name = attribute.getName();
		Object value = attribute.getValue();
		try {
			if (Name.equals("Name")) {
				// if null value, try and see if the setter returns any
				// exception
				if (value == null) {
					name = null;
					// if non null value, make sure it is assignable to the
					// attribute
				} else if ((Class.forName("java.lang.String"))
						.isAssignableFrom(value.getClass())) {
					name = (String) value;
				}
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public AttributeList getAttributes(String[] attributeNames) {
		if (attributeNames == null)
			return null;
		AttributeList resultList = new AttributeList();
		// if attributeNames is empty, return an empty result list
		if (attributeNames.length == 0)
			return resultList;
		for (int i = 0; i < attributeNames.length; i++) {
			try {
				Object value = getAttribute(attributeNames[i]);
				resultList.add(new Attribute(attributeNames[i], value));
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		return resultList;
	}

	public AttributeList setAttributes(AttributeList attributes) {
		if (attributes == null)
			return null;
		AttributeList resultList = new AttributeList();
		// if attributeNames is empty, nothing more to do
		if (attributes.isEmpty())
			return resultList;
		// for each attribute, try to set it and add to the result list if
		// successfull
		for (Iterator i = attributes.iterator(); i.hasNext();) {
			Attribute attr = (Attribute) i.next();
			try {
				setAttribute(attr);
				String name = attr.getName();
				Object value = getAttribute(name);
				resultList.add(new Attribute(name, value));
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		return resultList;
	}

	public Object invoke(String operationName, Object params[],
			String signature[]) throws MBeanException, ReflectionException {
		// Check for a recognized operation name and call the corresponding
		// operation
		if (operationName.equals("print")) {
			// 具体实现我们的操作方法print
			System.out.println("Hello, " + name + ", this is HellDynamic!");
			dynamicAddOperation();
			return null;
		} else if (operationName.equals("print1")) {
			System.out.println("这是动态增加的一方法print1");
			return null;
		} else {
			// unrecognized operation name:
			throw new ReflectionException(new NoSuchMethodException(
					operationName), "Cannot find the operation "
					+ operationName + " in " + className);
		}
	}

	public MBeanInfo getMBeanInfo() {
		return mBeanInfo;
	}
}

 说明：

·         实现于接口DynamicMBean

·         借助于各种辅助类完成一个类的构造。构造函数类MBeanConstructorInfo、属性类MBeanAttributeInfo、方法类MBeanOperationInfo

          ·这里所有public方法是实现于DynamicMBean的。主要提供：setAttribute设置属性、getAttribute取得属性、setAttributes设置一组属性、getAttributes取得一组属性、invoke方法调用、getMBeanInfo　MBeanServer由这个方法得到关键的MBean类的构造信息。 

 

 2.HelloAgent

package jmx.dynamicmbean;
import javax.management.MBeanServer;
import javax.management.MBeanServerFactory;
import javax.management.ObjectName;

import com.sun.jdmk.comm.HtmlAdaptorServer;
/**
 * 该类是一个Agent类，说明： 先创建了一个MBeanServer，用来做MBean的容器
 * 将Hello这个类注入到MBeanServer中，注入需要创建一个ObjectName类
 * 创建一个AdaptorServer，这个类将决定MBean的管理界面，这里用最普通的Html型界面。 AdaptorServer其实也是一个MBean。
 * jmx.hello:name=Hello的名字是有一定规则的，格式为：“域名:name=MBean名称”，
 * 域名和MBean名称都可以任意取。 打开网页：http://localhost:8082/
 * @author chenyw
 *
 */
public class HelloAgent {
    public static void main(String[] args) throws Exception {
    	// 创建一个MBeanServer，用来做MBean的容器
        MBeanServer server = MBeanServerFactory.createMBeanServer();
        ObjectName helloName = new ObjectName("chengang:name=HelloDynamic");
        HelloDynamic hello = new HelloDynamic();
     // 将Hello这个类注入到MBeanServer中，注入需要创建一个ObjectName类
        server.registerMBean(hello, helloName);
        ObjectName adapterName = new ObjectName("HelloAgent:name=htmladapter,port=8082");
        HtmlAdaptorServer adapter = new HtmlAdaptorServer();
        server.registerMBean(adapter, adapterName);
        adapter.start();
        System.out.println("start.....");
    }
} 

 

3.运行

先运行HelloAgent。再打开浏览器，输入网址：http://localhost:8082/。单击进入“name=HelloDynamic ”项，执行print方法后再回到上一页面你会发现又多了一个print1方法。

 

4、总结

动态MBean的代码稍显复杂，但对于一些特殊需求的情况，它将显示出强大威力。而且它还是模型MBeans（Model MBeans）的基础。不过在一般的项目中，动态MBean还是用得比较少，所谓利器深藏之而不用，非常时方现光芒。