Creating an MBean (Method 2)

The second way to create an MBean is the single createMBean method of the MBean server. In this case, the MBean server instantiates the class and registers it all at once. As a result, the caller never has a direct reference to the new object.

Example 5-3 Creating an MBean (Method 2)

ObjectInstance httpConnectorInstance = null;
try {
    String httpConnectorClassName = "com.sun.jdmk.comm.HttpConnectorServer";
    // Let the HTTP connector server provides its default name
    httpConnectorInstance =
        myMBeanServer.createMBean(httpConnectorClassName, null);
} catch(Exception e) {
    e.printStackTrace();
    System.exit(0);
}
// We need the object name to refer to our MBean
ObjectName httpConnectorName = httpConnectorInstance.getObjectName();
println("CLASS NAME  = " + httpConnectorInstance.getClassName());
println("OBJECT NAME = " + httpConnectorName.toString());

// Now we demonstrate the bulk getter of the MBean server
try {
    String att1 = "Protocol";
    String att2 = "Port";
    String attNames[]= {att1, att2};
    AttributeList attList =
        myMBeanServer.getAttributes(httpConnectorName, attNames);
    Iterator attValues = attList.iterator();
    println(att1 + "\t=" + ((Attribute) attValues.next()).getValue());
    println(att2 + "\t=" + ((Attribute) attValues.next()).getValue());

} catch (Exception e) {
    e.printStackTrace();
    System.exit(0);
}

// Now we explicitly start the HTTP connector server
try {
    myMBeanServer.invoke(httpConnectorName, "start",
                         new Object[0], new String[0]);

    // waiting to leave starting state...
    while (new Integer(CommunicatorServer.STARTING).equals
           (myMBeanServer.getAttribute(httpConnectorName,"State"))) {
        sleep(1000);
    }
    println("STATE = " + 
         myMBeanServer.getAttribute(httpConnectorName, "StateString"));
} catch (Exception e) {
    e.printStackTrace();
    System.exit(0);
}
[...]

The advantage of this method for creating MBeans is that the instantiation and registration are done in one call. In addition, if we have registered any class loaders in the MBean server, they will automatically be used if the class is not available locally. See "The M-Let Class Loader" for more information on class loading.

The createMBean method has several forms, some with parameters for class constructors and some without. In this examples we don't give any parameters for the constructor because we wish to use the default constructor that takes no arguments. If your MBean class has no default constructor, you must use a form that allows you to pass parameters to a constructor.

The major difference is that we no longer have a reference to our MBean instance. The object instance that was only used for display purposes in the previous example now gives us the only reference we have on the MBean: its object name.

What can be seen as a drawback of this method is that all management of the new MBean must now be done through the MBean server. For the attributes of the MBean, we need to call the generic getter and setter of the MBean server, and for the operations we need to call the invoke method. When the agent needs to access the MBean, having to go through the MBean server adds some complexity to the code. It does have the advantage of not relying on any shortcuts provided by the MBean, making the code more portable and reusable.

However, the createMBean method is ideal for quickly launching new MBeans that the agent application doesn't need to manipulate. In just one call, the new objects are instantiated and exposed for management.