Java Server Faces (JSF) is "Swing for server-side applications". It presents a dynamically controlled sequence of screens through the user's web browser. Forms in the web screen can have widgets that the user can use to send data to the application. The data is sent when the user clicks on a form button. The application can respond by sending a new screen to the browser. An example login application can be run here.

JSF has these parts:

• Data management using Java
• A set of prefabricated UI components that are translated into standard HTML tags so that they can be used with any browser
• A component model that enables third-party developers to supply additional components

Some earlier web technologies intermingle HTML and code from programming languages such as Java. JSF keeps different languages in different files. JSF is well-supported by IDEs such as NetBeans and Eclipse.

There are two structures associated with a JSF application.

• Application developers work in an IDE such as NetBeans or Eclipse. The IDE imposes a development structure. It uses a build script to produce the WAR file from the development structure.
• The application is deployed as a WAR file. The JSF framework imposes a deployment structure on its contents.

A JSF application is deployed as a WAR file. The structure of the WAR file is similar to the development structure except that Java source files are replaced by Java class files.

The WAR file for the login application has this structure:

In NetBeans the login application appears in the Projects pane as:

The Configuration Files folder is not shown expanded in the above screenshot. It contains the same files as the Web Pages/WEB-INF folder.

Unlike JSF, some earlier web technologies intermingle HTML and programming language code. Disadvantages include:

• It fails to separate models and views.

• Professional web designers prefer not to deal with embedded code.

• Professional programmers are notoriously unqualified for graphic design.

• Model-View-Controller Architecture

  • View components are "wired" to Model through beans.
  • JSF acts as Controller, processing action and value change events.

• Data Conversion

  • Change textual web form data into numbers, dates, and other data types.

• Validation and Error Handling

  • Detect missing or incorrect input.
  • Display appropriate error messages.

• Internationalization

  • Use resource bundles to give web pages different text depending on locale.

• Custom Components

  • Let application programmers develop their own components when JSF components are not enough.

• AJAX Support

  • Give application programmers use of tools to reduce the number of screens by moving some processing to the browser.

• Alternative Renderers

  • e.g., for WML or XUL pages.

This is a simplified life cycle of a JSF request initiated by the browser. The important fact for now is that request data is extracted, decoded, and verified.

With AJAX (Asynchronous JavaScript with XMLHttpRequest) the response need not be an HTML page. It can be information used by the browser to dynamically modify its current web page. JavaScript is the language used on the browser. XMLHttpRequest is a JavaScript function for asynchronous data transfer.