Page Navigation in JavaServer Faces
The Action Class
An Action is an object that performs a task. In JSF, an
Action is represented by the abstract
javax.faces.application.Action class.
The most important method here is invoke method, an abstract method that returns a String.
Its signature is as follows:
public abstract String invoke()
You write the code to perform the task for this Action object
in this method. The JSF implementation will call your invoke
method.
An Action can be invoked by a UICommand via the
actionRef attribute of its command_button or
command_hyperlink tags. For an instruction on how to use this
class, see the example in the section "Conditional Page Navigation."
Simple Navigation
The following example illustrates the simplest navigation rule. This
application consists of two pages: page1.jsp and
page2.jsp. From page1.jsp, the user can click the
button to go to page2.jsp, and vice versa. The navigation rules in
Listing 1 specify the navigation from both page1.jsp and
page2.jsp.
<navigation-rule>
<from-tree-id>/page1.jsp</from-tree-id>
<navigation-case>
<to-tree-id>/page2.jsp</to-tree-id>
</navigation-case>
</navigation-rule>
<navigation-rule>
<from-tree-id>/page2.jsp</from-tree-id>
<navigation-case>
<to-tree-id>/page1.jsp</to-tree-id>
</navigation-case>
</navigation-rule>
The first navigation-rule element specifies the target for
page1.jsp. It contains the navigation-case element
with a to-tree-id sub-element, without a from-outcome
or a from-action-ref sub-element. This means that, regardless of the
outcome, target page (page2.jsp) will be displayed. The second
navigation rule specifies the target for page2.jsp. From
page2.jsp, the user will definitely go to
page1.jsp.
Note: the original page will be re-displayed if there is an error in
processing.
Both page1.jsp and page2.jsp use the
TestingBean. This bean is registered in the Application
Configuration file as follows:
<managed-bean>
<managed-bean-name>TestingBean</managed-bean-name>
<managed-bean-class>ch06.TestingBean</managed-bean-class>
<managed-bean-scope>session</managed-bean-scope>
</managed-bean>
page1.jsp contains a UIInput component and a
validator that forces the user to type four or more characters into the
UIInput component. The page1.jsp page is given in
Listing 6.
Listing 6. page1.jsp
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h"%>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f"%>
<html>
<head>
<title>Page 1</title>
</head>
<body>
<f:use_faces>
<h:form formName="myForm">
Enter your user name (minimum 4 characters) :
<h:input_text valueRef="TestingBean.value">
<f:validate_length minimum="4"/>
</h:input_text>
<br>
<h:command_button commandName="submit" label="submit"/>
<br>
<h:output_errors/>
</h:form>
</f:use_faces>
</body>
</html>
page2.jsp contains a UIOutput component
that displays the value entered by the user to the UIInput
component in the page1.jsp page. The page2.jsp page
also has a command button for the user to go back to the page1.jsp
page. The page2.jsp page is given in Listing 7.
Listing 7. page2.jsp
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h"%>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f"%>
<html>
<head>
<title>Page 2</title>
</head>
<body>
<f:use_faces>
<h:form formName="myForm">
Your user name is <h:output_text
valueRef="TestingBean.value"/>
<br>
<h:command_button commandName="back" label="Back"/>
</h:form>
</f:use_faces>
</body>
</html>
You can invoke the page1.jsp page using the following URL:
http://localhost:8080/JSFCh06/faces/page1.jsp
Now, type in a string of four or more characters. You should see
page2.jsp welcoming you. If you click the Back button, you will
see the page1.jsp page again.
Note that if you type less than four characters into the
UIInput component in page1.jsp page, the validator in
page1.jsp will add a Message object to the
FacesContext instance, and this will cause the navigation to be
cancelled. As a result, you will see the page1.jsp page again,
with an error message.