4、动态MBean：DynamicMBean

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。