JSF (JavaServer Faces)

JavaServer Pages (JSF) have been considered a major event in Java's web programming. With JSF, you can use web components on the web to capture events generated by user behavior. Not far more, Java Tools will support this technology, developing web applications will be similar to how we now develop Swing programs: drag and drop control, write event listeners. This article is a brief introduction of JSF, and provides an example of JSF to show event drive characteristics of JSF. To understand this article, you need to have a certain understanding of servlets, JSP, JavaBeans, with the label library.

First, a JSF application is a servlet / JSP application. It has a configuration descriptor, with a JSP page, customer custom label, static resource, and more. Different, JSF applications are event-driven. You determine the behavior of the application by writing an event listening class. Several steps need to establish a JSF application:

1. Establish a JSP page and package HTML elements with JSF components.

2. Write a JavaBean to keep the user to enter the status of component data.

3. Write an event listener to determine what should be reflected when the event occurs, such as the user clicks on a button or submits a form. JSF supports two events: ActionEvent and ValueChangeeevent. ActionEvent is for the user to submit a form and click button, and ValueChangeeevent is triggered when a JSF component changes.

Now let's take a look at the details of the JSF action.

What is JSF work?

The JSP page is a user interface for the JSF application. Each page includes some JSF components to describe web controls such as forms, input boxes, buttons, and more. Components can be embedded in another component, as the input box can be in the form. Each JSP page is represented as a component tree. JaveBeans get data and stores from the user's request.

This is interesting: Whenever the user does anything, if you click the button or submit a form, there is an event. The event message is then transmitted to the server via HTTP. At the server side, it is a Web container that is configured with a special servlet called Faces Servlet. Faces servlet (javax.faces.webapp.facesservlet) is an engine for all JSF applications. Each JSF application has a separate Faces Servlet in a web container. Another important object is javax.faces.context.facescontext, which includes all necessary information about the current user request.

The background processing of the Faces Servlet is quite complicated. However, you don't have to understand these details, just remember that the Faces Servlet creates a component tree for the JSP page, and the control of the component tree is correspondingly. Faces Servlet knows how to create a component tree because it has accessed all JSP pages in the current application. Faces Servlet also creates an EVENT object and passes it to all registered listeners. You can get the components of this page by FacesContext corresponding to the current request.

The event generated by the web control on the client browser is included in an HTTP request, and there is also other information such as browser types, request addresses. Therefore, all requests that need Faces Servlet processing must point to this servlet. Then how do you handle each HTTP request by calling Faces ServelT? It is easy, just use a servlet-mapping element with a servlet-maping element in the configuration descriptor to map to the Faces Servlet. Usually, you will use / faces / * style, as shown below:

faces servlet

javax.faces.webapp.facesservlet

1

faces servlet

/ faces / *

The request address must contain the style described in the element. This requirement is not easy to reach. It is also important to note that the element, which contains the Faces Servlet, has a element to determine if the application is loaded when the application is first started.

In order to capture the event generated by the component, you need to write a listener for this component and register it to this component. This can be done by embedding elements in the client tag indicating the component. For example, in order to let a run listener named jsfapp.myactionListener, the event generated by the command button called Submitbutton is captured, and the code as follows is written in your JSP page:

CommandName = "Submit">

An Action Listener must implement a javax.faces.event.ActionListener interface, and a value-change listner must implement a java.faces.event.valueChangeDLister interface. Let's create a simple JSF application to show how JSF is driven.

A simple JSF application

We will create a simple application that can be added to the two numbers. To run this app, you need to prepare Tomcat5 with JSF V1.0 EA4 (included in Java Web Services Developer Pack (JWSDP) 1.2). This app includes:

Adder.jsp JSP page.

Numberbean's JavaBean stores user data

MyActionListener event listener web.xml configuration description file

In order to make this application work normally, there are several JAR files, including JSF standard implementation and other class libraries. If you have a JWSDP 1.2, you can find these files you need under the JSFLIB directory. Copy these .jar files into the web-inf / lib directory. Here is the list of the entire .jar and .tld file:

JSF-API.JAR contains classes with Faces Servlet and other related javax.faces packets

JFS-ri.jar is the reference implementation of JSF

JSTL_L.JAR

Standard.jar

In addition, a JSF application requires the following libraries, which are part of the Apache Jakarta project:

Commons-beanutils.jar

Commons-digester.jar

Commons-logging.jar IS

The following few segments discuss each part of this JSF example. The last small segment, "compile and run", explain how JSF applications run.

Create a directory structure

First create a directory structure for your JSF application. In Tomcat, it is in a webApps directory. "Figure 1" describes the directory structure of an application called MyJSFAPP.

Write configuration descriptor

Like other Servlet / JSP applications, this application also requires a configuration description file. Such as "Listing 1" means.

Listing 1. The Deployment Descriptor (The Web.xml File)

"- // Sun Microsystems, Inc.//dtd Web Application 2.3 // En"

"http://java.sun.com/dtd/web-app_2_3.dtd" ;;>

faces servlet

javax.faces.webapp.facesservlet

1

faces servlet

/ faces / *

There are two parts in this configuration description file.

Element Registration Faces Servlet,

Elements declare that any request address containing / faces / model must be passed to the Faces Servlet.

Create a JSP page

A JSP page called Adder.JSP provides a user interface, such as "Listing 2":

Listing 2.jsp Page

<% @ Taglib Uri = "http://java.sun.com/jsf/html" ;;

prefix = "h"%>

<% @ Taglib URI = "http://java.sun.com/jsf/core" ;; prefix = "f"%>