Programming

The JMX Technology Programming Model


Using JMX to instrument your applications, services, or devices for manageability is simple. This is because JMX technology shares Java's object model. If you are familiar with Java and its JavaBeans component model, you already know 95% of all you need to know.
As mentioned previously, an MBean is a Java object that follows some standard design patterns and naming conventions. It can represent a device, application, or any resource that needs to be managed. An MBean exposes a management interface or a set of readable and/or writable attributes and a set of invokable operations, along with a self-description. Note that the management interface does not change through the life of an MBean instance.
Sample Application
This simple application manages a resource. You will create a simple standard MBean that exposes a String object and an operation. For more JMX technology examples, please see the JMX Tutorial.
The first step is to develop the MBean interface. In this application, the interface is called HelloMBean, which declares three methods: one getter, one setter, and one for saying hello as shown in Code Sample 1.
Code Sample 1: HelloMBean.java

Code:

      
    public interface HelloMBean {
     public void setMessage(String message);
     public String getMessage();     public void sayHello();
 }

The next step is to implement the MBean interface. A sample implementation is shown in the following Code Sample.
Code Sample 2: Hello.java

Code:

      
    public class Hello implements HelloMBean {
    private String message = null;
     public Hello() {
       message = "Hello there";
    }
     public Hello(String message) {
       this.message = message;
    }
     public void setMessage(String message) {
       this.message = message;
    }
     public String getMessage() {
       return message;
    }
     public void sayHello() {
       System.out.println(message);
    }
 }

Congratulations! You have created your first MBean. The next step is to test the MBean, by developing a JMX agent in which you register the MBean. A JMX agent is a component in the agent level and acts as a container for the MBean. A sample agent, SimpleAgent, is provided in Code Sample 3. This agent performs the following tasks:
Code Sample 3: SimpleAgent.java

Code:

      
    import javax.management.*;
 import java.lang.management.*;
  public class SimpleAgent {
    private MBeanServer mbs = null;
     public SimpleAgent() {        // Get the platform MBeanServer
        mbs = ManagementFactory.getPlatformMBeanServer();        // Unique identification of MBeans
       Hello helloBean = new Hello();
       ObjectName helloName = null;
        try {          // Uniquely identify the MBeans and register them with the platform MBeanServer
           helloName = new ObjectName("SimpleAgent:name=hellothere");
          mbs.registerMBean(helloBean, helloName);
       } catch(Exception e) {
          e.printStackTrace();
       }
    }     // Utility method: so that the application continues to run
    private static void waitForEnterPressed() {
       try {
          System.out.println("Press  to continue...");
          System.in.read();
       } catch (Exception e) {
          e.printStackTrace();
       }
     }
     public static void main(String argv[]) {
       SimpleAgent agent = new SimpleAgent();
       System.out.println("SimpleAgent is running...");
       SimpleAgent.waitForEnterPressed();
    }
 }

The java.lang.management.ManagementFactory class is a factory class for getting managed beans for the Java platform. In this example, the getPlatformMBeanServer() method is used to get the platform MBeanServer, which is the interface for MBean manipulation on the agent side. It contains the methods necessary for the creation, registration, and deletion of MBeans. The MBeanServer is the core component of the JMX agent infrastructure.
To experiment with this application, do the following:
6. Now, you can connect to the service. Once connected, select the MBeans tab so that
you can list the MBeans and manage them as shown in Figure 3.