ScanDirAgent.java

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/*
 * Copyright (c) 2006, 2011, Oracle and/or its affiliates. All rights reserved.
 *
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 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Oracle nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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/*
 * This source code is provided to illustrate the usage of a given feature
 * or technique and has been deliberately simplified. Additional steps
 * required for a production-quality application, such as security checks,
 * input validation and proper error handling, might not be present in
 * this sample code.
 */
 
 
package com.sun.jmx.examples.scandir;
 
import com.sun.jmx.examples.scandir.ScanManagerMXBean.ScanState;
import java.io.IOException;
import java.lang.management.ManagementFactory;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;
import javax.management.JMException;
import javax.management.Notification;
import javax.management.NotificationEmitter;
import javax.management.NotificationListener;
 
public class ScanDirAgent {
 
    private static final Logger LOG =
            Logger.getLogger(ScanDirAgent.class.getName());
 
    // Proxy to the ScanManagerMXBean - created by init();
    //
    private volatile ScanManagerMXBean proxy = null;
 
    // A queue to put received Notifications.
    //
    private final BlockingQueue<Notification> queue;
 
    // A listener that will put notifications into the queue.
    //
    private final NotificationListener listener;
 
    public ScanDirAgent() {
        // Initialize the notification queue
        queue = new LinkedBlockingQueue<Notification>();
 
        // Creates the listener.
        listener = new NotificationListener() {
            public void handleNotification(Notification notification,
                                           Object handback) {
                try {
                    // Just put the received notification in the queue.
                    // It will be consumed later on by 'waitForClose()'
                    //
                    LOG.finer("Queuing received notification "+notification);
                    queue.put(notification);
                } catch (InterruptedException ex) {
                    // OK
                }
            }
        };
    }
 
    public void init() throws IOException, JMException {
 
        // Registers the ScanManagerMXBean singleton in the
        // platform MBeanServer
        //
        proxy = ScanManager.register();
 
        // Registers a NotificationListener with the ScanManagerMXBean in
        // order to receive state changed notifications.
        //
        ((NotificationEmitter)proxy).addNotificationListener(listener,null,null);
    }
 
    public void cleanup() throws IOException, JMException {
        try {
            ((NotificationEmitter)proxy).
                    removeNotificationListener(listener,null,null);
        } finally {
            ManagementFactory.getPlatformMBeanServer().
                unregisterMBean(ScanManager.SCAN_MANAGER_NAME);
        }
    }
 
    public void waitForClose() throws IOException, JMException {
 
        // Wait until state is closed
        while(proxy.getState() != ScanState.CLOSED ) {
            try {
                // Wake up at least every 30 seconds - if we missed a
                // notification - we will at least get a chance to
                // call getState(). 30 seconds is obviously quite
                // arbitrary - if this were a real daemon - id'be tempted
                // to wait 30 minutes - knowing that any incoming
                // notification will wake me up anyway.
                // Note: we simply use the state change notifications to
                // react more quickly to state changes: see javadoc above.
                //
                queue.poll(30,TimeUnit.SECONDS);
            } catch (InterruptedException ex) {
                // OK
            }
        }
    }
 
    public static void main(String[] args)
        throws IOException, JMException {
        System.out.println("Initializing ScanManager...");
        final ScanDirAgent agent = new ScanDirAgent();
        agent.init();
        try {
            System.out.println("Waiting for ScanManager to close...");
            agent.waitForClose();
        } finally {
            System.out.println("Cleaning up...");
            agent.cleanup();
        }
    }
}