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Java Dynamic Management Kit 5.0 Tutorial

getMBeanInfo Method

Because the MBean description should never change, it is usually created one time only at instantiation, and the getMBeanInfo method simply returns its reference at every call. The MBean constructor should therefore build the MBeanInfo object from the MBean metadata classes such that it accurately describes the management interface. And since most dynamic MBeans will always be instantiated with the same management interface, building the MBeanInfo object is fairly straightforward.

Example 2–2 shows how the SimpleDynamic MBean defines its management interface, as built at instantiation and returned by its getMBeanInfo method:

Example 2–2 Implementation of the getMBeanInfo Method

// class constructor
public SimpleDynamic() {

    buildDynamicMBeanInfo();
}

// internal variables describing the MBean
private String dClassName = this.getClass().getName();
private String dDescription = "Simple implementation of a dynamic MBean.";

// internal variables for describing MBean elements
private MBeanAttributeInfo[] dAttributes = new MBeanAttributeInfo[2];
private MBeanConstructorInfo[] dConstructors = new MBeanConstructorInfo[1];
private MBeanOperationInfo[] dOperations = new MBeanOperationInfo[1];
private MBeanInfo dMBeanInfo = null;

// internal method
private void buildDynamicMBeanInfo() {

    dAttributes[0] = new MBeanAttributeInfo(
        "State",                 // name
        "java.lang.String",      // type
        "State: state string.",  // description
        true,                    // readable
        true);                   // writable
    dAttributes[1] = new MBeanAttributeInfo(
        "NbChanges",
        "java.lang.Integer",
        "NbChanges: number of times the State string has been changed.",
        true,
        false);

    // use reflection to get constructor signatures
    Constructor[] constructors = this.getClass().getConstructors();
    dConstructors[0] = new MBeanConstructorInfo(
        "SimpleDynamic(): No-parameter constructor",  //description
        constructors[0]);                  // the contructor object

    MBeanParameterInfo[] params = null;
    dOperations[0] = new MBeanOperationInfo(
        "reset",                     // name
        "Resets State and NbChanges attributes to their initial values",
                                     // description
        params,                      // parameter types
        "void",                      // return type
        MBeanOperationInfo.ACTION);  // impact

    dMBeanInfo = new MBeanInfo(dClassName,
                               dDescription,
                               dAttributes,
                               dConstructors,
                               dOperations,
                               new MBeanNotificationInfo[0]);
}

// exposed method implementing the DynamicMBean.getMBeanInfo interface
public MBeanInfo getMBeanInfo() {

    // return the information we want to expose for management:
    // the dMBeanInfo private field has been built at instantiation time,
    return(dMBeanInfo);
}