JavaMail: Keeping IMAPFolder.idle() alive

Question

I am making a program that needs to monitor a Gmail account for new messages, and in order to get them ASAP I am using JavaMail\'s idle feature. Here is a code snippet from

Answer 1

Actually the Java Mail samples include an IMAP IDLE example, which is as follows. Besides that, the IdleManager class might be interesting.

/*
 * Copyright (c) 1996-2010 Oracle and/or its affiliates. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * 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,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

import java.util.*;
import java.io.*;
import javax.mail.*;
import javax.mail.event.*;
import javax.activation.*;

import com.sun.mail.imap.*;

/* Monitors given mailbox for new mail */

public class monitor {

    public static void main(String argv[]) {
    if (argv.length != 5) {
        System.out.println(
        "Usage: monitor     ");
        System.exit(1);
    }
    System.out.println("\nTesting monitor\n");

    try {
        Properties props = System.getProperties();

        // Get a Session object
        Session session = Session.getInstance(props, null);
        // session.setDebug(true);

        // Get a Store object
        Store store = session.getStore("imap");

        // Connect
        store.connect(argv[0], argv[1], argv[2]);

        // Open a Folder
        Folder folder = store.getFolder(argv[3]);
        if (folder == null || !folder.exists()) {
        System.out.println("Invalid folder");
        System.exit(1);
        }

        folder.open(Folder.READ_WRITE);

        // Add messageCountListener to listen for new messages
        folder.addMessageCountListener(new MessageCountAdapter() {
        public void messagesAdded(MessageCountEvent ev) {
            Message[] msgs = ev.getMessages();
            System.out.println("Got " + msgs.length + " new messages");

            // Just dump out the new messages
            for (int i = 0; i < msgs.length; i++) {
            try {
                System.out.println("-----");
                System.out.println("Message " +
                msgs[i].getMessageNumber() + ":");
                msgs[i].writeTo(System.out);
            } catch (IOException ioex) { 
                ioex.printStackTrace(); 
            } catch (MessagingException mex) {
                mex.printStackTrace();
            }
            }
        }
        });

        // Check mail once in "freq" MILLIseconds
        int freq = Integer.parseInt(argv[4]);
        boolean supportsIdle = false;
        try {
        if (folder instanceof IMAPFolder) {
            IMAPFolder f = (IMAPFolder)folder;
            f.idle();
            supportsIdle = true;
        }
        } catch (FolderClosedException fex) {
        throw fex;
        } catch (MessagingException mex) {
        supportsIdle = false;
        }
        for (;;) {
        if (supportsIdle && folder instanceof IMAPFolder) {
            IMAPFolder f = (IMAPFolder)folder;
            f.idle();
            System.out.println("IDLE done");
        } else {
            Thread.sleep(freq); // sleep for freq milliseconds

            // This is to force the IMAP server to send us
            // EXISTS notifications. 
            folder.getMessageCount();
        }
        }

    } catch (Exception ex) {
        ex.printStackTrace();
    }
    }
}