Java Platform, Enterprise Edition (Java EE) 8 The Java EE Tutorial

## Referencing a Managed Bean Method

A component tag has a set of attributes for referencing managed bean methods that can perform certain functions for the component associated with the tag. These attributes are summarized in Table 11-7.

Table 11-7 Component Tag Attributes That Reference Managed Bean Methods

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

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 managed 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 oJavaServer Faces Facelets Tag Library documentation. For example, the definition of the `validator` attribute of the `inputText` tag 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 attributes.

### Referencing a Method That Performs Navigation

If your page includes a component, such as a button or a link, 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 managed bean method that performs some processing and returns a logical outcome `String`

The following example shows how to reference a navigation method:

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

See Writing a Method to Handle Navigation for information on how to write such a method.

### 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 managed bean method, you refer to the method by using the component’s `actionListener` attribute.

The following example shows how such a method could be referenced:

    <h:commandLink id="Duke" action="bookstore"
                   actionListener="#{actionBean.chooseBookFromLink}">

The `actionListener` attribute of this component tag references the `chooseBookFromLink` method using a method expression. The `chooseBookFromLink` method handles the event when the user clicks the link rendered by this component. See Writing a Method to Handle an Action Event for information on how to write such a method.

### Referencing a Method That Performs Validation

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

The following simplified example from The guessnumber-cdi CDI Example shows how to reference a method that performs validation on `inputGuess`, an input component:

    <h:inputText id="inputGuess"
        value="#{userNumberBean.userNumber}"
        required="true" size="3"
        disabled="#{userNumberBean.number eq userNumberBean.userNumber ...}"
        validator="#{userNumberBean.validateNumberRange}">
    </h:inputText>

The managed bean method `validateNumberRange` verifies that the input value is within the valid range, which changes each time another guess is made. See Writing a Method to Perform Validation for information on how to write such a method.

### 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 managed bean method instead of a `ValueChangeListener` implementation, you refer to the method by using the component’s `valueChangeListener` attribute:

    <h:inputText id="name"
                 size="30"
                 value="#{cashierBean.name}"
                 required="true"
                 valueChangeListener="#{cashierBean.processValueChange}" />
    </h:inputText>

The `valueChangeListener` attribute of this component tag references the `processValueChange` method of `CashierBean` by using a method expression. The `processValueChange` method handles the event of a user entering a 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 a `ValueChangeEvent`.

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