18.2 Overview of JSF Architecture


The architecture of JSF is not completely unlike other MVC architectures you've probably encountered when building web applications. In fact, some of its pieces should be quite familiar now that you've read this book. However, JFS adds functionality in several places where Struts is lacking, and it does so a way that separates interface from implementation. As stated earlier, this is an important (but often overlooked) quality.

Because it's built around the MVC concept, you might expect to see models, views, and controllers in JSF. And while these elements are all present in JSF, the web imposes some distinct limitations on the MVC model. Let's look at a simplified scenario of how a traditional MVC architecture works:

  1. The view responds to user actions by invoking methods on the controller.

  2. The controller interacts with the model and updates it.

  3. The model creates and publishes events that views and controllers respond to by updating themselves.

Unfortunately, these steps don't work in the web world. Web browsers rarely sit and wait for an event to be published. Instead, they make a request for information and then expect that information to be returned they are certainly not preconditioned to listen for events.

JSF's approach is to provide components to handle the controller aspects of the application. These include the FrontController (similar to the Struts ActionServlet), NavigationHandler, conversion and formatting components, ActionListeners to interpret the commands, and validate the presentation data. JSF also provides components for the view. These are implemented as client-specific rendering kits made up of renderers. These renderers know how to make items such as a buttons or text fields in a browser.

JSF contains these essential ingredients:


Reusable UI Components

Components for buttons, text fields, and other visual elements.


Renderers

For rendering data to the appropriate client type (e.g. HTML for web browsers).


Validation and Conversion

Tools to convert and validate client-specific types to Java types (e.g., user-entered text to a Java Date).


Component Tree

An in-memory representation of the user interface.

18.2.1 The JSF Request/Response Lifecycle

A JSF application supports two types of requests and two types of responses:


Faces request

A request sent from a previously generated JSF response.


Non-Faces request

A request sent to an application component such as a servlet or JSP.


Faces response

A response created by the rendering response phase of the JSF processing lifecycle.


Non-Faces response

A response that was not created by the rendering response phone (e.g., a JSP that doesn't include JSF components).

According to the specification, these different requests and responses result in three possible lifecycles for a JSF application:

  • Non-Faces request generates a Faces response

  • Faces request generates a non-Faces response

  • Faces request generates a Faces response (probably the most common)

Figure 18-1 illustrates the request/response lifecycle for the standard scenario.

Figure 18-1. The standard JSF request/response lifecycle
figs/jstr2_1801.gif


As mentioned earlier, there are more similarities than differences between JSF and Struts. The low-level components within JSF sound a great deal like the components included with the Struts tag libraries. In fact, there's a great deal of overlap between these seemingly disparate technologies, and Craig McClanahan has publicly announced that he plans on a seamless integration of JSF and Struts. The goal is to allow you to replace the use of some of the Struts tags in your application with UI components of JSF, while continuing to utilize the Struts Controller and Action classes. You might imagine how a JSF Front controller could pass a request on to the Struts RequestProcessor to perform some business service on its behalf. This process is indicated in the "Invoke application" step in Figure 18-1.



Programming Jakarta Struts
Programming Jakarta Struts, 2nd Edition
ISBN: 0596006519
EAN: 2147483647
Year: 2003
Pages: 180

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