Google Web Toolkit allows you to build AJAX apps in the Java language.

What is Google Web Toolkit?
Google Web Toolkit (GWT) is a Java development framework that lets you escape the matrix of technologies that make writing AJAX applications so difficult and error prone. With GWT, you can develop and debug AJAX applications in the Java language using the Java development tools of your choice. When you deploy your application to production, the GWT compiler to translates your Java application to browser-compliant JavaScript and HTML.

Here's the GWT development cycle:

Use your favorite Java IDE to write and debug an application in the Java language, using as many (or as few) GWT libraries as you find useful.
Use GWT's Java-to-JavaScript compiler to distill your application into a set of JavaScript and HTML files that you can serve with any web server.
Confirm that your application works in each browser that you want to support, which usually takes no additional work.

Why Translate Java Code to JavaScript?
Java technologies offer a productive development plaform, and with GWT, they can instantly become the basis of your AJAX development platform as well. Here are some of the benefits of developing with GWT:

You can use all of your favorite Java development tools (Eclipse, IntelliJ, JProfiler, JUnit) for AJAX development. Static type checking in the Java language boosts productivity while reducing errors. Common JavaScript errors (typos, type mismatches) are easily caught at compile time rather than by users at runtime.

Code prompting/completion is widely available. Automated Java refactoring is pretty snazzy these days. Java-based OO designs are easier to communicate and understand, thus making your AJAX code base more comprehensible with less documentation.

Here are some key features of "Google Web Toolkit":

· Dynamic, reusable UI components
· Create a Widget by compositing other Widgets. Lay out Widgets automatically in Panels. Send your Widget to other developers in a JAR file
· Really simple RPC
· To communicate from your web application to your web server, you just need to define serializable Java classes for your request and response. In production, GWT automatically serializes the request and deserializes the response from the server. GWT's RPC mechanism can even handle polymorphic class hierarchies, and you can throw exceptions across the wire
· Browser history management
· No, AJAX applications don't need to break the browser's back button. GWT lets you make your site more usable by easily adding state to the browser's back button history
· Real debugging
· In production, your code is compiled to JavaScript, but at development time it runs in the Java virtual machine. That means when your code performs an action like handling a mouse event, you get full-featured Java debugging, with exceptions and the advanced debugging features of IDEs like Eclipse
· Browser compatible
· Your GWT applications automatically support IE, Firefox, Mozilla, Safari, and Opera with no browser detection or special-casing within your code in most cases
· Interoperability and fine-grained control
· If GWT's class library doesn't meet your needs, you can mix handwritten JavaScript in your Java source code using our JavaScript Native Interface (JSNI)

What's New in This Release: [ read full changelog ]

· Fixed “Operation Aborted” errors during startup on IE6/7.
· Fixed a minor security issue affecting the benchmark reporting system. We'd like to thank Daiki Fukumori of Secure Sky Technology, Inc. for reporting this.
· Hosted mode does not work properly on Mac OS X 10.5 (Leopard). Please see the FAQ Entry: Can I use GWT 1.4 On Mac OS X 10.5 (Leopard)? for links to an unofficial build for Leopard users.