Google Web Toolkit

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Google Web Toolkit (GWT /ˈɡwɪt/)) 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.[1]

GWT emphasizes reusable, efficient solutions to recurring Ajax challenges, namely asynchronous remote procedure calls, history management, bookmarking, Internationalization and cross-browser portability.



GWT version 1.0 RC 1 (build 1.0.20) was released on May 16, 2006[2]. Google announced GWT at the JavaOne conference, 2006.[3]

Release history:

  • GWT 1.0 May 17, 2006
  • GWT 1.1 August 11, 2006
  • GWT 1.2 November 16, 2006
  • GWT 1.3 February 5, 2007
  • GWT 1.4 August 28, 2007
  • GWT 1.5 August 27, 2008
  • GWT 1.6 April 07, 2009
  • GWT 1.7 July 13, 2009
  • GWT 2.0 December 08, 2009

Development with GWT

Using GWT, developers can rapidly 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.

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. In live presentations, the developers of GWT emphasize that "GWT is not its libraries" and that it only includes a library but is not fundamentally yet another AJAX library. This open-ended philosophy sometimes surprises developers new to GWT who expect it to provide an end-to-end "on rails" application framework. 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:

  • 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.
  • Web mode: The application is run as pure JavaScript and HTML, compiled from the Java source. This mode is typically used for deployment.

Google provides a plugin for Eclipse which handles most GWT related tasks in the IDE, including creating projects, invoking the GWT compiler, creating GWT launch configurations, validations, syntax highlighting, etc.

Several open-source plugins are available for making GWT development easier with other IDEs. E.g., GWT4NB for NetBeans, Cypal Studio for GWT, Eclipse and JDeveloper etc.


The major GWT components include:

GWT Java-to-JavaScript Compiler
Translates the Java programming language to the JavaScript programming language.
GWT Hosted Web Browser
Allows the developers to run and execute GWT applications in hosted mode (the app runs as Java in the JVM without compiling to JavaScript). It is commonly used for debugging.
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.


  • 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.[4]
  • Simple RPC mechanism
  • Browser history management
  • Support for full-featured Java debugging[3]
  • GWT handles all cross-browser issues for the developer.[3]
  • JUnit integration
  • Easy internationalization
  • 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).[4] 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 easy to understand or obfuscated and smaller to download.[4]
  • A number of libraries are available for GWT, by Google and third parties. These extend GWT's features.[4]

Available widgets

As of version 1.4 (August 2007), GWT offers several widgets:[5]

  • HTML primitives (Button, Radio Button, Checkbox, TextBox, PasswordTextBox, TextArea, Hyperlink, ListBox, Table etc.)
  • PushButton, ToggleButton
  • MenuBar
  • Tree
  • TabBar
  • DialogBox
  • Panels (PopupPanel, StackPanel, HorizontalPanel, VerticalPanel, FlowPanel, VerticalSplitPanel, HorizontalSplitPanel, DockPanel, TabPanel, DisclosurePanel)
  • RichTextArea
  • SuggestBox (auto-complete)

The Google Web Toolkit Incubator has additional widgets undergoing development (and likely to be released in future versions of GWT).

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.

GWT 2.0

On Dec 08, 2009 Google launched Google Web Toolkit 2.0 with Speed Tracer.[6][7]

Version 2.0 of GWT will offer a number of new features[8], 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.

See also



External links

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