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 8-4.

Table 8-4 Component Tag Attributes That Reference Backing Bean Methods

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

The component tag refers to a backing bean method using a method expression as a value of one of the attributes. The method referenced by an attribute must follow a particular signature, which is defined by the tag attribute’s definition in the TLD. For example, the definition of the validator attribute of the inputText tag in html_basic.tld is the following:

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

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

• Referencing a Method That Performs Navigation

• Referencing a Method That Handles an Action Event

• Referencing a Method That Performs Validation

• Referencing a Method That Handles a Value-Change Event

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 following examples shows how to reference a navigation method:

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

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 following example shows how the method is referenced:

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

The actionListener attribute of this component tag references the chooseLocaleFromLink method using a method expression. The chooseLocaleFromLink method handles the event when user clicks the hyperlink rendered by this component.

Referencing a Method That Performs Validation

If the input of one of the components on your page is validated by a backing bean method, refer to the method from the component’s tag using the validator attribute.

The following example shows how to reference a method that performs validation on email, an input component:

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

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 following example shows how a component references a ValueChangeListener implementation that handles the event when a user enters a name in the name input filed:

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

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 expression. The processValueChange method handles the event of a user entering a name in the input field rendered by this component.