一、前言
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：
二、实例
1、HelloDynamic类
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;
/**
* @author Sunny Peng
* @author change by Chen.Gang, add a feature for dynamic add operation
* @version 1.0
*/
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类
前面说了HelloDynamic和普通MBean的使用方法是一样的，因此HelloAgent和第一篇的HelloAgent基本一样，就是把Hello改成HelloDynamic而已。为了实例完整，也一并帖出来吧。
import javax.management.MBeanServerFactory;
import javax.management.ObjectName;
import com.sun.jdmk.comm.HtmlAdaptorServer;
public class HelloAgent {
public static void main(String[] args) throws Exception {
MBeanServer server = MBeanServerFactory.createMBeanServer();
ObjectName helloName = new ObjectName("chengang:name=HelloDynamic");
HelloDynamic hello = new HelloDynamic();
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。