【JMX】3. 动态MBean
复习
一共有四种MBean：
- 标准MBeans（Standard MBeans）设计和实现是最简单的，这类MBean使用自己的方法名作为管理接口；——在前一篇中的Hello、HelloMBean就是一个标准MBeans（Standard MBeans）
- 动态MBeans（Dynamic MBeans）必须实现一个指定的接口，由于动态MBeans在运行期间暴露它们的管理接口，因此更为灵活；
- 开放MBeans（Open MBeans）属于动态MBeans，这类MBean依靠基础数据类型来实现通用管理，并为友情用户进行自我声明；
- 模型MBeans（Model MBeans）同样也是动态MBeans，这类MBeans是完全可配置的，在运行期间进行自我声明；它们为资源动态工具提供一个一般性的，有默认行为的MBeans类。
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。
1）编写动态MBean
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.", //String description,
true, true, false); //boolean isReadable,boolean isWritable,boolean isIs
//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", //String description,
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);
}
@Override
public Object getAttribute(String attribute_name) {
if (attribute_name != null)
return null;
if (attribute_name.equals("Name"))
return name;
return null;
}
@Override
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();
}
}
@Override
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;
}
@Override
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;
}
@Override
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();
System.out.println("added a dynamic operation(print1)!");
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);
}
}
@Override
public MBeanInfo getMBeanInfo() {
return mBeanInfo;
}
}
2）编写Agent
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。
public class HelloAgent {
public static void main(String[] args) throws Exception {
//先创建了一个MBeanServer，用来做MBean的容器
// MBeanServer server = MBeanServerFactory.createMBeanServer();
MBeanServer server = ManagementFactory.getPlatformMBeanServer();
ObjectName helloName = new ObjectName("alpha-dynamic:name=HelloWorld");
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);
//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。
// alpha:name=HelloWorld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。
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。
start..... Hello, null, this is HellDynamic! added a dynamic operation(print1)! 这是动态增加的一方法print1
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。