Referencing a Backing Bean Method - The J2EE 1.4 Tutorial

Referencing a Backing Bean Method

A component tag has a set of attributes for referencing backing bean methods that can perform certain functions for the component associated with the tag. These attributes are summarized in Table 18-10.

Table 18-10 Component Tag Attributes that Reference Backing Bean Methods 

Attribute	Function
action	Refers to a backing bean method that performs navigation processing for the component and returns a logical outcome String
actionListener	Refers to a backing bean method that handles action events
validator	Refers to a backing bean method that performs validation on the component's value
valueChangeListener	Refers to a backing bean method that handles value-change events

Only components that implement ActionSource can use the action and actionListener attributes. Only UIInput components or components that extend UIInput can use the validator or valueChangeListener attributes.

The component tag refers to a backing bean method using a method-binding expression as a value of one of the attributes. The following four sections give examples of how to use the four different attributes.

Referencing a Method That Performs Navigation

If your page includes a component (such as a button or hyperlink) that causes the application to navigate to another page when the component is activated, the tag corresponding to this component must include an action attribute. This attribute does one of the following

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

The bookcashier.jsp page of the Duke's Bookstore application has a commandButton tag that refers to a backing bean method that calculates the shipping date. If the customer has ordered more than $100 (or 100 euros) worth of books, this method also sets the rendered properties of some of the components to true and returns null; otherwise it returns receipt, which causes the bookreceipt.jsp page to display. Here is the commandButton tag from the bookcashier.jsp page:

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

The action attribute uses a method-binding expression to refer to the submit method of CashierBean. This method will process the event fired by the component corresponding to this tag.

Writing a Method to Handle Navigation describes how to implement the submit method of CashierBean.

The application architect must configure a navigation rule that determines which page to access given the current page and the logical outcome, which is either returned from the backing bean method or specified in the tag. See Configuring Navigation Rules for information 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 that event is handled by a backing bean method, you refer to the method by using the component's actionListener attribute.

The chooselocale.jsp page of the Duke's Bookstore application includes some components that generate action events. One of them is the NAmerica component:

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

The actionListener attribute of this component tag references the chooseLocaleFromLink method using a method-binding expression. The chooseLocaleFromLink method handles the event of a user clicking on the hyperlink rendered by this component.

The actionListener attribute can be used only with the tags of components that implement ActionSource. These include UICommand components.

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 validated by a backing bean method, you refer to the method from the component's tag using the validator attribute.

The Coffee Break application includes a method that performs validation of the email input component on the checkoutForm.jsp page. Here is the tag corresponding to this component:

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

This tag references the validate method described in Writing a Method to Perform Validation using a method-binding expression.

The validator attribute can be used only with UIInput components or those components whose classes extend UIInput.

Writing a Method to Perform Validation describes how to implement a method that performs validation.

Referencing a Method That Handles a Value-change Event

If you want a component on your page to generate a value-change event and you want that event to be handled by a backing bean method, you refer to the method using the component's valueChangeListener attribute.

The name component on the bookcashier.jsp page of the Duke's Bookstore application references a ValueChangeListener implementation that handles the event of a user entering a name in the name input field:

<h:inputText 
  id="name" 
  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 bean method instead of a listener implementation class. To refer to this backing bean method, the tag uses the valueChangeListener attribute:

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

The valueChangeListener attribute of this component tag references the processValueChange method of CashierBean using a method-binding expression. The processValueChange method handles the event of a user entering his name in the input field rendered by this component.

The valueChangeListener attribute can be used only with the tags of UIInput components and components whose classes extend UIInput.

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

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