Create the Hello MBean and QueueSampler MXBean, register them in the platform MBean server
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/*
* Main.java - main class for the Hello MBean and QueueSampler MXBean example.
* Create the Hello MBean and QueueSampler MXBean, register them in the platform
* MBean server, then wait forever (or until the program is interrupted).
*/
import java.beans.ConstructorProperties;
import java.lang.management.ManagementFactory;
import java.util.Date;
import java.util.Queue;
import java.util.concurrent.ArrayBlockingQueue;
import javax.management.AttributeChangeNotification;
import javax.management.MBeanNotificationInfo;
import javax.management.MBeanServer;
import javax.management.Notification;
import javax.management.NotificationBroadcasterSupport;
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 Hello MBean we will register
ObjectName mbeanName = new ObjectName("com.example:type=Hello");
// Create the Hello World MBean
Hello mbean = new Hello();
// Register the Hello World MBean
mbs.registerMBean(mbean, mbeanName);
// Construct the ObjectName for the QueueSampler MXBean we will register
ObjectName mxbeanName = new ObjectName("com.example: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, mxbeanName);
// Wait forever
System.out.println("Waiting for incoming requests...");
Thread.sleep(Long.MAX_VALUE);
}
}
/*
* 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.
*/
interface QueueSamplerMXBean {
public QueueSample getQueueSample();
public void clearQueue();
}
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;
}
}
/*
* Hello.java - MBean implementation for the Hello MBean. This class must
* implement all the Java methods declared in the HelloMBean interface, with the
* appropriate behavior for each one.
*/
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();
}
}
}/*
* HelloMBean.java - MBean interface describing the management operations and
* attributes for the Hello World MBean. In this case there are two
* operations, "sayHello" and "add", and two attributes, "Name" and
* "CacheSize".
*/
interface HelloMBean {
// -----------
// operations
// -----------
public void sayHello();
public int add(int x, int y);
// -----------
// attributes
// -----------
// a read-only attribute called Name of type String
public String getName();
// a read-write attribute called CacheSize of type int
public int getCacheSize();
public void setCacheSize(int size);
}
class Hello extends NotificationBroadcasterSupport implements HelloMBean {
public void sayHello() {
System.out.println("hello, world");
}
public int add(int x, int y) {
return x + y;
}
/*
* Getter for the Name attribute. The pattern shown here is frequent: the
* getter returns a private field representing the attribute value. In our
* case, the attribute value never changes, but for other attributes it might
* change as the application runs. Consider an attribute representing
* statistics such as uptime or memory usage, for example. Being read-only
* just means that it can't be changed through the management interface.
*/
public String getName() {
return this.name;
}
/*
* Getter for the CacheSize attribute. The pattern shown here is frequent: the
* getter returns a private field representing the attribute value, and the
* setter changes that field.
*/
public int getCacheSize() {
return this.cacheSize;
}
/*
* Setter for the CacheSize attribute. To avoid problems with stale values in
* multithreaded situations, it is a good idea for setters to be synchronized.
*/
public synchronized void setCacheSize(int size) {
int oldSize = this.cacheSize;
this.cacheSize = size;
/*
* In a real application, changing the attribute would typically have
* effects beyond just modifying the cacheSize field. For example, resizing
* the cache might mean discarding entries or allocating new ones. The logic
* for these effects would be here.
*/
System.out.println("Cache size now " + this.cacheSize);
/*
* Construct a notification that describes the change. The "source" of a
* notification is the ObjectName of the MBean that emitted it. But an MBean
* can put a reference to itself ("this") in the source, and the MBean
* server will replace this with the ObjectName before sending the
* notification on to its clients.
*
* For good measure, we maintain a sequence number for each notification
* emitted by this MBean.
*
* The oldValue and newValue parameters to the constructor are of type
* Object, so we are relying on Tiger's autoboxing here.
*/
Notification n = new AttributeChangeNotification(this, sequenceNumber++,
System.currentTimeMillis(), "CacheSize changed", "CacheSize", "int",
oldSize, this.cacheSize);
/*
* Now send the notification using the sendNotification method inherited
* from the parent class NotificationBroadcasterSupport.
*/
sendNotification(n);
}
@Override
public MBeanNotificationInfo[] getNotificationInfo() {
String[] types = new String[] { AttributeChangeNotification.ATTRIBUTE_CHANGE };
String name = AttributeChangeNotification.class.getName();
String description = "An attribute of this MBean has changed";
MBeanNotificationInfo info = new MBeanNotificationInfo(types, name,
description);
return new MBeanNotificationInfo[] { info };
}
private final String name = "Reginald";
private int cacheSize = DEFAULT_CACHE_SIZE;
private static final int DEFAULT_CACHE_SIZE = 200;
private long sequenceNumber = 1;
}
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