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Referencing a Backing Bean Method

A component tag has a set of attributes for referencing backing bean methodsthat can perform certain functions for the component associated with the tag. Theseattributes are summarized inTable 11-10.

Table 11-10 Component Tag Attributes That Reference Backing Bean Methods

Attribute	Function
`action`	Refers to a backing bean method that performsnavigation processing for the component and returns a logical outcome`String`
`actionListener`	Refers to abacking bean method that handles action events
`validator`	Refers to a backing bean methodthat performs validation on the component’s value
`valueChangeListener`	Refers to a backing bean method thathandles value-change events

Only components that implementActionSource can use theaction andactionListener attributes. Only componentsthat implementEditableValueHolder can use thevalidator orvalueChangeListener attributes.

The component tag refers to a backing bean method using a method expressionas a value of one of the attributes. The method referenced by anattribute must follow a particular signature, which is defined by the tag attribute’sdefinition in the TLD. For example, the definition of thevalidator attribute of theinputText tag inhtml_basic.tld is the following:

void validate(javax.faces.context.FacesContext,     javax.faces.component.UIComponent, java.lang.Object)

The following four sections give examples of how to use the fourdifferent attributes.

Referencing a Method That Performs Navigation

If your page includes a component (such as a button or hyperlink) thatcauses the application to navigate to another page when the component is activated,the tag corresponding to this component must include anaction attribute. This attribute doesone of the following

Specifies a logical outcomeString that tells the application which page to access next
References a backing bean method that performs some processing and returns a logical outcomeString

Thebookcashier.jsp page of the Duke’s Bookstore application has acommandButton tag thatrefers to a backing bean method that calculates the shipping date. If thecustomer has ordered more than $100 (or 100 euros) worth of books, thismethod also sets therendered properties of some of the components totrue and returnsnull; otherwise it returnsreceipt, which causes thebookreceipt.jsp page todisplay. Here is thecommandButton tag from thebookcashier.jsp page:

<h:commandButton    value="#{bundle.Submit}"    action="#{cashier.submit}" />

Theaction attribute uses a method expression to refer to thesubmit methodofCashierBean. This method will process the event fired by the component correspondingto this tag.

Writing a Method to Handle Navigation describes how to implement thesubmit method ofCashierBean.

The application architect must configure a navigation rule that determines which page toaccess given the current page and the logical outcome, which is either returnedfrom the backing bean method or specified in the tag. SeeConfiguring Navigation Rules forinformation on how to define navigation rules in the application configuration resource file.

Referencing a Method That Handles an Action Event

If a component on your page generates an action event, and if thatevent is handled by a backing bean method, you refer to the methodby using the component’sactionListener attribute.

Thechooselocale.jsp page of the Duke’s Bookstore application includes some components that generateaction events. One of them is theNAmerica component:

<h:commandLink action="bookstore"     actionListener="#{localeBean.chooseLocaleFromLink}">

TheactionListener attribute of this component tag references thechooseLocaleFromLink method using amethod expression. ThechooseLocaleFromLink method handles the event of a user clicking on thehyperlink rendered by this component.

Writing a Method to Handle an Action Event describes how to implement a method that handles an action event.

Referencing a Method That Performs Validation

If the input of one of the components on your page is validatedby a backing bean method, you refer to the method from the component’stag using thevalidator attribute.

The Coffee Break application includes a method that performs validation of theemailinput component on thecheckoutForm.jsp page. Here is the tag corresponding tothis component:

<h:inputText value="#{checkoutFormBean.email}"    size="25" maxlength="125"    validator="#{checkoutFormBean.validateEmail}"/>

This tag references thevalidate method described inWriting a Method to Perform Validation using a method expression.

Referencing a Method That Handles a Value-change Event

If you want a component on your page to generate a value-change eventand you want that event to be handled by a backing beanmethod, you refer to the method using the component’svalueChangeListener attribute.

Thename component on thebookcashier.jsp page of the Duke’s Bookstore application referencesaValueChangeListener implementation that handles the event of a user entering aname in thename input field:

<h:inputText         size="50"     value="#{cashier.name}"     required="true">    <f:valueChangeListener type="listeners.NameChanged" /></h:inputText>

For illustration,Writing a Method to Handle a Value-Change Event describes how to implement this listener with a backing beanmethod instead of a listener implementation class. To refer to this backing beanmethod, the tag uses thevalueChangeListener attribute:

<h:inputText         size="50"     value="#{cashier.name}"     required="true"    valueChangeListener="#{cashier.processValueChange}" /></h:inputText>

ThevalueChangeListener attribute of this component tag references theprocessValueChange method ofCashierBeanusing a method expression. TheprocessValueChange method handles the event of a userentering his name in the input field rendered by this component.

Writing a Method to Handle a Value-Change Event describes how to implement a method that handles aValueChangeEvent.