Java Dynamic Management Kit 5.1 Tutorial

5.7 Managing MBeans

In 5.5 Creating an MBean Using the createMBean Method, you rely totally on the MBean server to create and access an MBean. You get attributes and invoke operations through the MBean server. Here we will concentrate on the usage of MBean metadata classes when accessing MBeans that represent resources.

We will rely on the StandardAgent and DynamicAgent classes presented in Part I. As mentioned in 2.3.1 Comparison With the SimpleStandard Example, the two are nearly identical. The same code works for any registered MBean, whether standard or dynamic. We examine the method for displaying MBean metadata that is common to both.

Example 5–3 Processing MBean Information

private MBeanServer server = null; // assigned by MBeanServerFactory

private void printMBeanInfo(ObjectName mbeanObjectName, String mbeanName) {

    echo("    using the getMBeanInfo method of the MBeanServer");
    sleep(1000);
    MBeanInfo info = null;
    try {
         info = server.getMBeanInfo(mbeanObjectName);
    } catch (Exception e) {
          echo("\t!!! Could not get MBeanInfo object for " +
               mbeanName + " !!!");
          e.printStackTrace();
          return;
    }
    echo("\nCLASSNAME: \t"+ info.getClassName());
    echo("\nDESCRIPTION: \t"+ info.getDescription());
    echo("\nATTRIBUTES");
    MBeanAttributeInfo[] attrInfo = info.getAttributes();
    if (attrInfo.length>0) {
        for(int i=0; i<attrInfo.length; i++) {
            echo(" ** NAME: \t"+ attrInfo[i].getName());
            echo("    DESCR: \t"+ attrInfo[i].getDescription());
            echo("    TYPE: \t"+ attrInfo[i].getType() +
                 "\tREAD: "+ attrInfo[i].isReadable() +
                 "\tWRITE: "+ attrInfo[i].isWritable());
        }
    } else echo(" ** No attributes **");

    echo("\nCONSTRUCTORS");
    MBeanConstructorInfo[] constrInfo = info.getConstructors();
    for(int i=0; i<constrInfo.length; i++) {
        echo(" ** NAME: \t"+ constrInfo[i].getName());
        echo("    DESCR: \t"+ constrInfo[i].getDescription());
        echo("    PARAM: \t"+ constrInfo[i].getSignature().length +
                 " parameter(s)");
    }

    echo("\nOPERATIONS");
    MBeanOperationInfo[] opInfo = info.getOperations();
    if (opInfo.length>0) {
        for(int i=0; i<constrInfo.length; i++) {
            echo(" ** NAME: \t"+ opInfo[i].getName());
            echo("    DESCR: \t"+ opInfo[i].getDescription());
            echo("    PARAM: \t"+ opInfo[i].getSignature().length +
                     " parameter(s)");
        }
    } else echo(" ** No operations ** ");

    echo("\nNOTIFICATIONS");
    MBeanNotificationInfo[] notifInfo = info.getNotifications();
    if (notifInfo.length>0) {
        for(int i=0; i<constrInfo.length; i++) {
            echo(" ** NAME: \t"+ notifInfo[i].getName());
            echo("    DESCR: \t"+ notifInfo[i].getDescription());
            String notifTypes[] = notifInfo[i].getNotifTypes();
            for (int j = 0; j < notifTypes.length; j++) {
                echo("    TYPE: \t" + notifTypes[j]);
            }
        }
    } else echo(" ** No notifications **");
}

The getMBeanInfo method of the MBean server gets the metadata of an MBean's management interface and hides the MBean's implementation. This method returns an MBeanInfo object that contains the MBean's description. We can then get the lists of attributes, operations, constructors, and notifications to display their descriptions. Recall that the dynamic MBean provides its own meaningful descriptions and that the standard MBean descriptions are default strings provided by the introspection mechanism of the MBean server.