Abhijeeti's Blog

Session handling is pretty common in web applications. Java Servlet technology provides an API for managing sessions and allows several mechanisms for implementing sessions.  But if you have swing application and want to track the session how to do that?

Here is the scenario – Suppose you have a swing based kiosk application. User logs in to the application and does some operations.  Now for some reason he doesn’t perform any operation for 3-4 minutes then for security reasons we need to somehow log out from the swing application.

This can be achieved with the help of Swing timers and AWT default toolkit.

Here are the steps

• When user logs in start the swing timer by passing SESSION_TIMEOUT value and ActionListener (to handle timeout event).
• Add AWTEventListener to AWT toolkit with AWTEvent.MOUSE_EVENT_MASK and AWTEvent.KEY_EVENT_MASK. This will track only mouse events and key events.
• Whenever AWT event occurs (that means user performed some action) restart the timer.
• When the system is idle for SESSION_TIMEOUT time, timer will call actionPerformed method of its ActionListener.It means session timeout occured and you need to logout.

import java.awt.AWTEvent;
import java.awt.Toolkit;
import java.awt.event.AWTEventListener;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.Timer;

/**
 * @author airaj
 *
 */
public class SystemTimeoutClient implements AWTEventListener, ActionListener
{
    private int SESSION_TIMEOUT = 240000; // 4 minutes
    private static SystemTimeoutClient client = null;
    private Timer timer;

    private SystemTimeoutClient()
    {
    }

    public static SystemTimeoutClient getSystemTimeoutClient()
    {
        if (client == null)
        {
            client = new SystemTimeoutClient();
        }
        return client;
    }

    public void trackSessionTimeout()
    {
        timer = new Timer(SESSION_TIMEOUT, this);
        timer.setInitialDelay(SESSION_TIMEOUT);
        timer.setRepeats(false);
        timer.start();
        trackSystemEvents();
    }

    public void stopSessionTracking()
    {
        if (timer.isRunning())
        {
            timer.stop();
        }
    }

    private void trackSystemEvents()
    {
        Toolkit.getDefaultToolkit().addAWTEventListener(this, AWTEvent.MOUSE_EVENT_MASK + AWTEvent.KEY_EVENT_MASK);
    }

    @Override
    public void eventDispatched(AWTEvent event)
    {
        // User action detected. Restart the timer
        if (timer.isRunning())
        {
            timer.restart();
        }
    }

    @Override
    public void actionPerformed(ActionEvent e)
    {
        // Session Timeout occured. Close resources and log out from system. 

    }
}

If you want free online file storage then you can use  GMail Drive. It creates a virtual file system around your Google GMail account, allowing you to use GMail as a storage medium. It enables you to save and retrieve files stored on your GMail account directly from inside Windows Explorer. It adds a new drive to your computer under the My Computer folder, where you can copy and drag n drop files.

Here are the steps you can follow

• Create one Gmail account for your storage. You can use your existing Gmail account but its better to have separate account for your online file storage.

• Download and install GMail drive shell extension from here

• After installation you will see new GMail Drive

• Double click on GMail Drive it will prompt for your GMail credentials

• After login you can copy files which you want to store into your new GMail drive.

• Now if you want to access your files from some other machine you can setup GMail Drive and you will have access to all those files.

• You can also access those files from your GMail account. Login to your account and you will see a separate message for each one of your file as an attachment.

I recently changed my primary domain for my blog to http://abhijeetiraj.com . It was really easy to do this change from wordpress’s Domain setting section.

If you do not have domain you can register new one from wordpress $14.97  per year. Check here for more information.

Recently we migrated from Backbase based portal to Spring MVC based portal for our kiosk transaction system. This will evolve as Offline system (see davids post on this here).

We mainly used Spring to build this offline system because it’s lightweight, easy to use, easy to test and it allows to configure and compose complex application from simpler components.

Here is the technology stack which we are using to build this offline system

• Spring MVC: Part of spring and MVC  based Framework for building robust web applications

• Spring Webflow: Built on Spring MVC and provides the infrastructure for building and running rich web application.

• JQuery: Fast and concise JavaScript Library that simplifies HTML document traversing, event handling, animating, and Ajax interactions for rapid web development.

• Blueprintcss: CSS framework which aims to cut down on your development time.

• JMesa: Dynamic HTML table rendering API/Tag library that allows you to filter, sort, paginate, export and edit your data however you need to.

• Sitemesh: Web-page layout and decoration framework and web-application integration framework to aid in creating large sites consisting of many pages for which a consistent look/feel, navigation and layout scheme is required.

• Hibernate: Powerful, high performance object/relational persistence and query service.

• Maven: Software project build and  management tool.

• MySQL: Most popular open source database.

• SpringSource ToolSuite: Eclipse-powered development environment for building Spring-powered enterprise applications.

Even though swing is very important part of the Java platform, truth is that its not thread safe. That means swing component methods called from multiple threads can cause thread interference or memory consistency errors. There are some exceptions to this. There are some swing component methods which are “thread safe” which can be safely invoked from any thread.

Reason why swing is not thread safe is that any attempt to create a thread-safe GUI library faces some fundamental problems. For more on this issue, see the following entry in Graham Hamilton’s blog: MultiThreaded toolkits: A failed dream?

Because of this swing event handling code execution as well as component repaint happens on a special thread known as the event dispatch thread. All the Swing component methods which are not thread safe must be invoked from this event dispatch thread. Programs that ignore this rule may function correctly most of the time, but are subject to unpredictable errors that are difficult to reproduce.

There are two fundamental things to understand about Swing and threads:

1. Time-consuming tasks should not be run on the Event Dispatch Thread. Otherwise the application becomes unresponsive. The EDT is busy executing your task and hence can’t process GUI events.
2. Swing components should be accessed on the Event Dispatch Thread only. To access components from other threads, you must use SwingUtilities. invokeAndWait, SwingUtilities. invokeLater or SwingWorker.