Java Dynamic Management Kit 5.0 Tutorial

Managing MBeans

In Creating an MBean (Method 2), we rely totally on the MBean server to create and access an MBean. The code example in that section demonstrates how to 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 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 8–5 Processing MBean Information

private MBeanServer server = null; // assigned by MBeanServerFactory

private void printMBeanInfo(ObjectName name) {

    echo("Getting the management information for  " + name.toString() );
    MBeanInfo info = null;

    try {
        info = server.getMBeanInfo(name);
    } catch (Exception e) {
        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();
    // Note: the class necessarily has at least one constructor
    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());
        }
    } 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.