Wednesday, December 30, 2009

MBean Descriptors

JMX MBean/MXBean get accessed by different clients(Ex: JConsole, VisualVM, and etc.,), where it is our responsibility that to explain/descirbe the details of the Bean, it includes

  • MBean author, version and etc.,
  • Attribute display name, type, minValue, maxValue, defaultValue and recommendedValue and its behaviour
  • Operation display name, and its argument details

Java SE 6 has come up integrated way of annotation approach for all types of MBean, where we can specify the additional details, is called Descriptors.

Author.java
package com.example.mxbeans; 
 
import java.lang.annotation.Documented; 
import java.lang.annotation.ElementType; 
import java.lang.annotation.Retention; 
import java.lang.annotation.RetentionPolicy; 
import java.lang.annotation.Target; 
import javax.management.DescriptorKey; 
 
@Documented 
@Target(ElementType.TYPE) 
@Retention(RetentionPolicy.RUNTIME) 
public @interface Author { 
    @DescriptorKey("Author") 
    String value(); 
} 

HelloWorldMXBean.java

package com.example.mxbeans; 
 
@Author("Krishna")
public interface HelloWorldMXBean { 
    @DisplayName("GETTER: Name") 
    public QueueSample getName(); 
    @DisplayName("OPERATION: clearHelloCount") 
    public void clearCount(); 
} 

In runtime these metadata/annotation converts in to JAVA object, for most constructors in the classes MBean*Info (MBeanInfo, MBeanAttributeInfo, and so on), a parallel constructor exists with the same parameters plus an additional javax.management.Descriptor parameter. The same is true for OpenMBean*InfoSupport. The MBean*Info and OpenMBean*InfoSupport classes contain a getDescriptor() method.

Read: MBean Descriptors Tutorial

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