Google Web Toolkit (GWT) is an open source Java software development framework that allows web developers to create Ajax applications in Java. It is licensed under the Apache License version 2.0.

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

History

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

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

Development

Using GWT, the 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 compiler deciphers the Java application to browser-compliant JavaScript and HTML.In effect GWT is a widget creation framework but it is not a complete GUI framework since there are many issues that it does not tackle but leaves a lot to the developer;for example; though GWT will give you history tokens when you click back or forward in the browser but it does not address how you can translate the token to an application state. (An inherited problem in AJAX)

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.

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

A command-line utility shipped with GWT, applicationCreator, automatically generates all the files needed to start a GWT project. It can also generate Eclipse project files. Several open-source plugins are available for making GWT development easier with IDEs. E.g., GWT4NB for NetBeans, Cypal Studio for GWT for Eclipse, gwtDeveloper for JDeveloper etc.

Components

The major GWT components include:GWT Java-to-JavaScript CompilerTranslates the Java programming language to the JavaScript programming language.
GWT Hosted Web BrowserAllows the developers to run and execute GWT applications in hosted mode (the app runs as Java in the JVM without compiling to JavaScript).
JRE emulation libraryJavaScript implementations of the frequently 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 libraryA 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 all cross-browser issues for the developer.

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). Common JavaScript errors (such as typos and type mismatches are caught at compile time.

JavaScript that the GWT compiler generates is quite obfuscated or very difficult to read, which provide the application with some security and protection of proprietary material.

A number of libraries are available for GWT, by Google and third parties. These extend GWTs features.

Criticism

GWT compiles JavaScript and HTML from Java bytecode. This model will in most scenarios create much larger JavaScript and HTML than what is possible to achieve with solutions where the JavaScript Widgets handcoded from before and is thought of rather as an API than as a "compiler result". An alternative way of creating an Ajax framework with "no-JavaScript pain capability" is to think of the browser as a purely rendering mechanism for predefined widgets and send messages from the server to those widgets and vice versa, see ZK_Framework.

Existing widgets

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

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)

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