Introduction

The basic idea of JDBQueue is to have a persistence Queue. Then, if the program need to restart, the queue is restored. We use a database because serialize a Queue objet is not faster, for each insertion.

This messages in the queue has 2 states:

• PENDING: It waits for a worker poll the message.
• PROGRESS: A worker is trying to work on the message.

There is a third-party state, that it is when the message are handled and it is completed. The work do completeTask and the message are removed from the DBQueue (persistence queue).

Download

You can download the source code from github and compile by yourself with Maven 3.

Or on the other hand, you can use a compiled version: https://dl.dropbox.com/u/2859837/JDBQueue-v0.1.zip

It contains all bindings to work with sqlite4java. You should choose the one for your platform, for instance, sqlite4java-win32-x86.dll.

Example 1

In order to handle the message an implementation of ITask should be provided. Moreover, to poll the messages automatically, a JDBWorker need to be created.

DBQueue q = new DBQueue("queue.db");
JDBWorker worker = new JDBWorker(q,new TestTask());
worker.start();

q.add("Test");
q.add("Test2");
q.poll();
q.take();

worker.join();

Example 2

class TestTask implements ITask
{
    private DBQueue queue; 
    public TestTask(DBQueue queue )
    {
        this.queue = queue;
    }
    public void handlerMessage(MessageObj message) {

        System.out.println(message);
        queue.completedTask(message.getId());

    }

}
public void workerTest()
{

    DBQueue q = new DBQueue("queue.db");


    JDBWorker worker = new JDBWorker(q,new TestTask(q), 500);
    worker.start();

    for (int i = 0 ; i<10 ; i++)
    {
        q.add("je1");
        q.add("je2");
        q.add("je3");
        System.out.println("Size: " + q.size());
        System.out.println("Size of pending " + q.sizePending());
        System.out.println("Size of progress " +q.sizeProgress());
        q.add("je4");
        q.add("je5");

    }
    while(q.size()>0)
    {
         System.out.println("Size: " + q.size());
        System.out.println("Size of pending " + q.sizePending());
        System.out.println("Size of progress " +q.sizeProgress());
        try {
            Thread.sleep(100);
        } catch (InterruptedException ex) {
            Logger.getLogger(WorkerTest.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
    System.out.println("Closing? " + q.size());
    worker.close();
    try {
        worker.join();
    } catch (InterruptedException ex) {
        Logger.getLogger(WorkerTest.class.getName()).log(Level.SEVERE, null, ex);
    }

}

}

Dependence

In order to grant the persistence, JDBQueue uses sqlite4java.

Notes

This work is still working in progress and used by a project. Generalization might be necessary to other cases. Feel free to contribute back to it.

Author

Luís A. Bastião Silva luis.kop@gmail.com

Licence

Copyright 2012 - Luís A. Bastião Silva

JDBQueue is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

JDBQueue is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with JDBQueue. If not, see http://www.gnu.org/licenses/.