動態MBean：DynamicMBean

五柳-先生發表於2015-10-21
Bean
一、前言
　
　　動態MBean是在執行期才定義它的屬性和方法，也就是說它有什麼屬性和方法是可以動態改變的。動態MBean主要利用一些輔助類（建構函式類MBeanConstructorInfo、屬性類MBeanAttributeInfo、方法類MBeanOperationInfo）來完成這個功能，所有的動態MBean必須實現DynamicMBean介面。DynamicMBean寫好後，使用方法和第一篇文章中普通的MBean一樣。
　
　　給出一個動態MBean的例項，這個例項最初動態構了一個Name屬性及一個print方法，當我們執行它的print方法之後，又給此MBean新增了一個print1方法。例項的程式碼如下：
二、例項
1、HelloDynamic類

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 {
    //這是我們的屬性名稱
    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() {
        //設定建構函式
        Constructor[] thisconstructors = this.getClass().getConstructors();
        constructors[0] = new MBeanConstructorInfo("HelloDynamic(): Constructs a HelloDynamic object", thisconstructors[0]);
        //設定一個屬性
        attributes[0] = new MBeanAttributeInfo("Name", "java.lang.String", "Name: name string.", true, true, false);
        //operate method 我們的操作方法是print
        MBeanParameterInfo[] params = null;//無引數
        operations[0] = new MBeanOperationInfo("print", "print(): print the name", params, "void", MBeanOperationInfo.INFO);
        mBeanInfo = new MBeanInfo(className, description, attributes, constructors, operations, mBeanNotificationInfoArray);
    }

    //動態增加一個print1方法
    private void dynamicAddOperation() {
        init();
        operations = new MBeanOperationInfo[2];//設定陣列為兩個
        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")) {
            //具體實現我們的操作方法print 
            System.out.println("Hello, " + name + ", this is HellDynamic!");
            dynamicAddOperation();
            return null;
        } else if (operationName.equals("print1")) {
            System.out.println("這是動態增加的一方法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;
    }
}

 
說明：

    * 實現於介面DynamicMBean
    * 藉助於各種輔助類完成一個類的構造。建構函式類MBeanConstructorInfo、屬性類MBeanAttributeInfo、方法類MBeanOperationInfo
    * 這裡所有public方法是實現於DynamicMBean的。主要提供：setAttribute設定屬性、 getAttribute取得屬性、setAttributes設定一組屬性、getAttributes取得一組屬性、invoke方法呼叫、 getMBeanInfo　MBeanServer由這個方法得到關鍵的MBean類的構造資訊。

2、HelloAgent類
　　
　　前面說了HelloDynamic和普通MBean的使用方法是一樣的，因此HelloAgent和第一篇的HelloAgent基本一樣，就是把Hello改成HelloDynamic而已。為了例項完整，也一併帖出來吧。

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、執行
　
　　先執行HelloAgent。再開啟瀏覽器，輸入網址：http://localhost:8082/。單擊進入“name=HelloDynamic ”項，執行print方法後再回到上一頁面你會發現又多了一個print1方法。
　
4、總結

　　動態MBean的程式碼稍顯複雜，但對於一些特殊需求的情況，它將顯示出強大威力。而且它還是模型MBeans（Model MBeans）的基礎。不過在一般的專案中，動態MBean還是用得比較少，所謂利器深藏之而不用，非常時方現光芒。

轉載： http://www.blogjava.net/hengheng123456789/articles/66375.html

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