[JMX一步步来]　4、动态MBean：DynamicMBean-白红宇

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：。单击进入“ ”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。

作者简介

陈刚，广西桂林人，著作有《Eclipse从入门到精通》

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posted on 2006-03-07 15:03 阅读(5320) 所属分类:

re: [JMX一步步来]　4、动态MBean：DynamicMBean

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

应该是

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

(attribute_name != null) 改为(attribute_name == null)

re: [JMX一步步来] 4、动态MBean：DynamicMBean

re: [JMX一步步来]　4、动态MBean：DynamicMBean