16 MXBeans

This example demonstrates the use of MXBeans. The source code contained in this section is used to create corresponding files in the examples/ directory specified in the appropriate setup procedure and includes:

• README file

• Main

• QueueSample

• QueueSampler

• QueueSamplerMXBean

examples/MXBean/README

# ==============================================================================
#
#  JMX Tutorial Introductory Example : Instrumenting Your Own Applications.
#                                      Using MXBeans.
#
#  The aim of this introductory example is to show the basic features of
#  the JMX technology first by instrumenting a simple resource using the new
#  type of MBean, i.e. MXBeans, and second by performing operations on it using
#  the jconsole tool. This example shows the implementation of an MXBean, how to
#  register it in the Platform MBean Server and how to perform remote operations
#  on it by connecting to the RMI connector server using the jconsole tool. The
#  goal of this example is to show a simple MXBean that manages a resource of
#  type Queue<String>. The MXBean declares a getter getQueueSample that takes
#  a snapshot of the queue when invoked and returns a Java class QueueSample
#  that bundles the following values together: the time the snapshot was taken,
#  the queue size and the head of the queue at that given time. The MXBean also
#  declares an operation clearQueue that clears all the elements in the queue
#  being managed. The example also shows how to register this MXBean in the
#  Platform MBean Server alongside the MBeans you can already see in jconsole.
#  This examples also shows how the existing Platform MBean Server can be
#  shared between the JVM and the application itself to register the application
#  MBeans, thus avoiding the creation of multiple MBean Server instances on the
#  same JVM.
#
# ==============================================================================
#
# In order to compile and run the example, make a copy of this README file, and
# then simply cut and paste all the commands as needed into a terminal window.
#
# This README makes the assumption that you are running under Java SE 6 on Unix,
# you are familiar with the JMX technology, and with the bourne shell or korn
# shell syntax.
#
# All the commands below are defined using Unix korn shell syntax.
#
# If you are not running Unix and korn shell you are expected to be able to
# adapt these commands to your favorite OS and shell environment.
#

# Compile Java classes
#
# The Java classes used in this example are contained in the com.example.mxbeans
# Java package.
#
# * Main.java: gets the Platform MBean Server, and creates
#              and registers the QueueSampler MXBean on it.
#
# * QueueSampler.java: implements the QueueSampler MXBean.
#
# * QueueSamplerMXBean.java: the management interface exposed
#                            by the QueueSampler MXBean.
#
# * QueueSample.java: the Java type returned by the getQueueSample()
#                     method in the QueueSampler MXBean interface.
#

javac com/example/mxbeans/*.java

# Start the Main application
#

java com.example.mxbeans.Main

# Start jconsole on a different shell window on the same machine
#
# JConsole is located in $(J2SE_HOME)/bin/jconsole
#

jconsole

# ==============================================================================

examples/MXBean/com/example/mxbeans/Main.java

/**
 * Main.java - main class for QueueSampler example. Create the Queue Sampler
 * MXBean, register it, then wait forever (or until the program is interrupted).
 */

package com.example.mxbeans;

import java.lang.management.ManagementFactory;
import java.util.Queue;
import java.util.concurrent.ArrayBlockingQueue;
import javax.management.MBeanServer;
import javax.management.ObjectName;

public class Main {
    /* For simplicity, we declare "throws Exception".  Real programs
       will usually want finer-grained exception handling.  */
    public static void main(String[] args) throws Exception {
        // Get the Platform MBean Server
        MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();

        // Construct the ObjectName for the MBean we will register
        ObjectName name =
                new ObjectName("com.example.mxbeans:type=QueueSampler");

        // Create the Queue Sampler MXBean
        Queue<String> queue = new ArrayBlockingQueue<String>(10);
        queue.add("Request-1");
        queue.add("Request-2");
        queue.add("Request-3");
        QueueSampler mxbean = new QueueSampler(queue);

        // Register the Queue Sampler MXBean
        mbs.registerMBean(mxbean, name);

        // Wait forever
        System.out.println("Waiting...");
        Thread.sleep(Long.MAX_VALUE);
    }
}

examples/MXBean/com/example/mxbeans/QueueSamplerMXBean.java

/**
 * QueueSamplerMXBean.java - MXBean interface describing the management
 * operations and attributes for the QueueSampler MXBean. In this case
 * there is a read-only attribute "QueueSample" and an operation "clearQueue".
 */

package com.example.mxbeans;

public interface QueueSamplerMXBean {
    public QueueSample getQueueSample();
    public void clearQueue();
}

examples/MXBean/com/example/mxbeans/QueueSampler.java

/**
 * QueueSampler.java - MXBean implementation for the QueueSampler MXBean.
 * This class must implement all the Java methods declared in the
 * QueueSamplerMXBean interface, with the appropriate behavior for each one.
 */

package com.example.mxbeans;

import java.util.Date;
import java.util.Queue;

public class QueueSampler implements QueueSamplerMXBean {

    private Queue<String> queue;

    public QueueSampler(Queue<String> queue) {
        this.queue = queue;
    }

    public QueueSample getQueueSample() {
        synchronized (queue) {
            return new QueueSample(new Date(), queue.size(), queue.peek());
        }
    }

    public void clearQueue() {
        synchronized (queue) {
            queue.clear();
        }
    }
}

examples/MXBean/com/example/mxbeans/QueueSample.java

/**
 * QueueSample.java - Java type representing a snapshot of a given queue.
 * It bundles together the instant time the snapshot was taken, the queue
 * size and the queue head.
 */

package com.example.mxbeans;

import java.beans.ConstructorProperties;
import java.util.Date;

public class QueueSample {

    private final Date date;
    private final int size;
    private final String head;

    @ConstructorProperties({"date", "size", "head"})
    public QueueSample(Date date, int size, String head) {
        this.date = date;
        this.size = size;
        this.head = head;
    }

    public Date getDate() {
        return date;
    }

    public int getSize() {
        return size;
    }

    public String getHead() {
        return head;
    }
}