另外还有两类 MBean：Open MBean 和 Model MBean。实际上它们也都是动态 MBean。
Open MBean 与其它动态 MBean 的唯一区别在于，前者对其公开接口的参数和返回值有所限制 —— 只能是基本类型或者 >javax.management.openmbean 包内的 ArrayType、CompositeType、TarbularType 等类型。这主要是考虑到管理系统的分布，很可能远端管理系统甚至 MBServer 层都不具有 MBean 接口中特殊的类。
Model Bean
然而，普通的动态 Bean 通常缺乏一些管理系统所需要的支持：比如持久化 MBean 的状态、日志记录、缓存等等。如果让用户去一一实现这些功能确实是件枯燥无聊的工作。为了减轻用户的负担，JMX 提供商都会提供不同的 ModelBean 实现。其中有一个接口是 Java 规范中规定所有厂商必须实现的：：>javax.management.modelmbean.RequiredModelBean。通过配置 Descriptor 信息，我们可以定制这个 Model Bean， 指定哪些 MBean 状态需要记入日志、如何记录以及是否缓存某些属性、缓存多久等等。这里，我们以 RequiredModelBean 为例讨论 ModelBean。比如，我们先来看一个例子，首先是 server 端：
package modelmbean;
public class Server {
private long startTime;
public Server() { }
public int start(){
startTime = System.currentTimeMillis();
return 0;
}
public long getUpTime(){
return System.currentTimeMillis() - startTime;
}
}
然后我们对它的监测如下：
package modelmbean;
import javax.management.*;
import javax.management.modelmbean.*;
public class Main {
public static void main(String[] args) throws Exception{
MBeanServer mBeanServer = MBeanServerFactory.createMBeanServer();
RequiredModelMBean serverMBean =
(RequiredModelMBean) mBeanServer.instantiate(
"javax.management.modelmbean.RequiredModelMBean");
ObjectName serverMBeanName =
new ObjectName("server: id=Server");
serverMBean.setModelMBeanInfo(getModelMBeanInfoForServer(serverMBeanName));
Server server = new Server();
serverMBean.setManagedResource(server, "ObjectReference");
ObjectInstance registeredServerMBean =
mBeanServer.registerMBean((Object) serverMBean, serverMBeanName);
serverMBean.invoke("start",null, null);
Thread.sleep(1000);
System.out.println(serverMBean.getAttribute("upTime"));
Thread.sleep(5000);
System.out.println(serverMBean.getAttribute("upTime"));
}
private static ModelMBeanInfo getModelMBeanInfoForServer(ObjectName objectName)
throws Exception{
ModelMBeanAttributeInfo[] serverAttributes =
new ModelMBeanAttributeInfo[1];
Descriptor upTime =
new DescriptorSupport(
new String[] {
"name=upTime",
"descriptorType=attribute",
"displayName=Server upTime",
"getMethod=getUpTime",
});
serverAttributes[0] =
new ModelMBeanAttributeInfo(
"upTime",
"long",
"Server upTime",
true,
false,
false,
upTime);
ModelMBeanOperationInfo[] serverOperations =
new ModelMBeanOperationInfo[2];
Descriptor getUpTimeDesc =
new DescriptorSupport(
new String[] {
"name=getUpTime",
"descriptorType=operation",
"class=modelmbean.Server",
"role=operation"
});
MBeanParameterInfo[] getUpTimeParms = new MBeanParameterInfo[0];
serverOperations[0] = new ModelMBeanOperationInfo("getUpTime",
"get the up time of the server",
getUpTimeParms,
"java.lang.Long",
MBeanOperationInfo.ACTION,
getUpTimeDesc);
Descriptor startDesc =
new DescriptorSupport(
new String[] {
"name=start",
"descriptorType=operation",
"class=modelmbean.Server",
"role=operation"
});
MBeanParameterInfo[] startParms = new MBeanParameterInfo[0];
serverOperations[1] = new ModelMBeanOperationInfo("start",
"start(): start server",
startParms,
"java.lang.Integer",
MBeanOperationInfo.ACTION,
startDesc);
ModelMBeanInfo serverMMBeanInfo =
new ModelMBeanInfoSupport(
"modelmbean.Server",
"ModelMBean for managing an Server",
serverAttributes,
null,
serverOperations,
null);
//Default strategy for the MBean.
Descriptor serverDescription =
new DescriptorSupport(
new String[] {
("name=" objectName),
"descriptorType=mbean",
("displayName=Server"),
"type=modelmbean.Server",
"log=T",
"logFile=serverMX.log",
"currencyTimeLimit=10" });
serverMMBeanInfo.setMBeanDescriptor(serverDescription);
return serverMMBeanInfo;
}
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