Google Web Toolkit

Google Web Toolkit (GWT ) is an open source set of tools that allows web developers to create and maintain complex JavaScript front-end applications in Java. Other than a few native libraries, everything is Java source that can be built on any supported platform with the included GWT Ant build files. It is licensed under the Apache License version 2.0.

GWT emphasizes reusable, efficient approaches to common web development tasks, namely asynchronous remote procedure calls, history management, bookmarking, UI abstraction, internationalization, and cross-browser portability.

History
GWT version 1.0 RC 1 was released on May 16, 2006. Google announced GWT at the JavaOne conference, 2006.

In August 2010, Google acquired Instantiations, a company known for its focus on Eclipse Java developer tools, including GWT Designer, which is now bundled with Google Plugin for Eclipse.

With introduction of the Dart programming language, Google has reassured the GWT community that GWT will continue to be supported for the foreseeable future, but also hinted at a possible rapprochement between the two Google solutions for "structured web programming". They've also admitted however that a number of engineers previously working on GWT are now working on Dart.

Development with GWT
Using GWT, developers can develop and debug Ajax applications in the Java language using the Java development tools of their choice. When the application is deployed, the GWT cross-compiler translates the Java application to standalone JavaScript files that are optionally obfuscated and deeply optimized. When needed, JavaScript can also be embedded directly into Java code, using Java comments.

GWT does not revolve only around user interface programming; it is a general set of tools for building any sort of high-performance client-side JavaScript functionality. Indeed, many key architectural decisions are left completely to the developer. The GWT mission statement clarifies the philosophical breakdown of GWT's role versus the developer's role. History is an example of such: although GWT manages history tokens as users click Back or Forward in the browser, it does not prescribe how to map history tokens to an application state.

GWT applications can be run in two modes:
 * Development mode (formerly Hosted mode): The application is run as Java bytecode within the Java Virtual Machine (JVM). This mode is typically used for development, supporting hot swapping of code and debugging.
 * Production mode (formerly Web mode): The application is run as pure JavaScript and HTML, compiled from the Java source. This mode is typically used for deployment.

Several open-source plugins are available for making GWT development easier with other IDEs, including GWT4NB for NetBeans, Cypal Studio for GWT (an Eclipse plugin), and GWT Developer for JDeveloper. The Google Plugin for Eclipse handles most GWT related tasks in the IDE, including creating projects, invoking the GWT compiler, creating GWT launch configurations, validation, and syntax highlighting.

Components
The major GWT components include:
 * GWT Java-to-JavaScript Compiler
 * Translates the Java programming language to the JavaScript programming language.


 * GWT Development Mode
 * Allows the developers to run and execute GWT applications in development mode (the app runs as Java in the JVM without compiling to JavaScript). Prior to 2.0, GWT hosted mode provided a special-purpose "hosted browser" to debug your GWT code. In 2.0, the web page being debugged is viewed within a regular browser. Development mode is supported through the use of a native-code plugin called the Google Web Toolkit Developer Plugin for many popular browsers.


 * JRE emulation library
 * JavaScript implementations of the commonly used classes in the Java standard class library (such as most of the java.lang package classes and a subset of the java.util package classes).


 * GWT Web UI class library
 * A set of custom interfaces and classes for creating widgets.

Features

 * Dynamic and reusable UI components: programmers can use pre-designed classes to implement otherwise time-consuming dynamic behaviors, such as drag-and-drop or sophisticated visual tree structures.
 * Simple RPC mechanism
 * Browser history management
 * Support for full-featured Java debugging
 * GWT handles some cross-browser issues for the developer.
 * Unit testing integration
 * Support for Internationalization and localization
 * HTML Canvas support (subject to API changes)
 * The developers can mix handwritten JavaScript in the Java source code using the JavaScript Native Interface (JSNI).
 * Support for using Google APIs in GWT applications (initially, support for Google Gears)
 * Open-source
 * The developers can design and develop their application in a pure object-oriented fashion, since they're using Java (instead of JavaScript). Common JavaScript errors, such as typos and type mismatches, are caught at compile time.
 * The JavaScript that the GWT compiler generates can be tailored to be either unobfuscated and easier to understand or obfuscated and smaller to download.
 * A number of libraries are available for GWT, by Google and third parties. These extend GWT's features.

Available Widgets
As of version 2.4 (September 2011), GWT offers several widgets and panels.

Many common widgets not found in the GWT have been implemented in third-party libraries, such as Ext GWT, GWT Component Library, GWT-Ext, GWT Widget Library, GWTiger, Rocket GWT, Dojo, SmartGWT etc.

Enterprise Usage
GWT is widely used in the Enterprise space due to its leveraging of common enterprise technologies including Java, Apache Tomcat (or similar web container), Eclipse IDE, Internet Explorer, and Internationalization and Localization. Java-based GWT RIAs are easier to test using the existing JUnit testing framework and code coverage tools, compared to large applications written in Javascript. Because GWT allows compile time verification of images, CSS, and business logic, many common development defects are automatically discovered without need of the manual testing commonly required by RIAs.

While often used in non-advertised internal applications, Google has noted that some of its products are GWT based:
 * Orkut
 * Blogger
 * AdWords
 * Flights
 * Wallet
 * Offers
 * Groups

Other companies using GWT are listed on the GWT Reference List.

GWT 2.0
On Dec 08, 2009 Google launched Google Web Toolkit 2.0 with Speed Tracer.

Version 2.0 of GWT offers a number of new features, including:
 * In-Browser Development Mode (formerly known as Out Of Process Hosted Mode, OOPHM): prior to version 2.0, hosted mode used to embed a modified browser to allow running the bytecode version of the application during development. With version 2.0, hosted mode, renamed "development mode", allows using any (supported) browser to view the page being debugged, through the use of a browser plugin. The plugin communicates with the development mode shell using TCP/IP, which allows cross platform debugging (for example, debugging in Internet Explorer on Windows from a development mode shell running on a Linux machine).
 * Code splitting: with the developer providing "split points" in the source code, the GWT compiler will be able to split the JavaScript code into several small chunks instead of one big download. This will lead to reduced application startup time as the size of the initial download is decreased.
 * Declarative User Interface: using an XML format, the new feature known as UiBinder allows the creation of user interfaces through declaration rather than code. This allows clean separation of UI construction and behavior implementation.
 * Resource bundling: the ClientBundle interface will allow resources of any nature (images, CSS, text, binary) to be bundled together and transferred in one download, resulting in fewer round-trips to the server and hence lower application latency.

Since the new development mode removed most platform-specific code, the new version will be distributed as a unique archive, instead of one per supported platform as was the case with previous versions.

Mobile
As a general framework for making web apps, GWT is also capable of being used as a framework for making mobile and tablet apps, either by making the needed widgets and animations from scratch, or by using one of the mobile frameworks for GWT. An HTML5 app written in GWT can have separate views for Tablets and Mobile phones.

Some of the most common mobile GWT libraries
 * GwtMobile
 * gwt-mobile-webkit
 * jqm4gwt
 * m-gwt

Other frameworks

 * GWT-Platform, an annotation based Model-View-Presenter framework for GWT
 * Errai is a GWT-based framework for building rich web applications using next-generation web technologies. Built on-top of ErraiBus, the framework provides a unified federation and RPC infrastructure with true, uniform, asynchronous messaging across the client and server.
 * SmartGWT, a GWT framework with a comprehensive widget library and server side databinding capabilities
 * Vaadin, a similar framework, which is based on GWT
 * Sencha GXT, GWT port of the popular Ext JS UI Framework commonly used in Enterprise applications.
 * Pyjamas Pyjamas, a port of GWT to Python
 * RubyJS, a port of GWT to Ruby
 * ZK, a similar framework, which is also written in Java.
 * GWT-php, a port of GWT to Php.
 * Scala+GWT, compile Scala code for the browser via the GWT toolchain.