Binding a Component Value to an Implicit Object (The Java EE 5 Tutorial)

The Java EE 5 Tutorial

Binding a Component Value to an Implicit Object

One external data source that a value attribute can refer to is an implicit object.

The bookreceipt.jsp page of the Duke’s Bookstore application includes a reference to an implicit object from a parameter substitution tag:

<h:outputFormat title="thanks" value="#{bundle.ThankYouParam}">
    <f:param value="#{sessionScope.name}"/>
</h:outputFormat>

This tag gets the name of the customer from the session scope and inserts it into the parameterized message at the key ThankYouParam from the resource bundle. For example, if the name of the customer is Gwen Canigetit, this tag will render:

Thank you, Gwen Canigetit, for purchasing your books from us.

The name tag on the bookcashier.jsp page has the NameChanged listener implementation registered on it. This listener saves the customer’s name in the session scope when the bookcashier.jsp page is submitted. See Implementing Value-Change Listeners for more information on how this listener works. See Registering a Value-Change Listener on a Component to learn how the listener is registered on the tag.

Retrieving values from other implicit objects is done in a similar way to the example shown in this section. Table 11–9 lists the implicit objects that a value attribute can refer to. All of the implicit objects except for the scope objects are read-only and therefore should not be used as a value for a UIInput component.

Table 11–9 Implicit Objects


Implicit Object	What It Is
`applicationScope`	A `Map` of the application scope attribute values, keyed by attribute name
`cookie`	A `Map` of the cookie values for the current request, keyed by cookie name
`facesContext`	The `FacesContext` instance for the current request
`header`	A `Map` of HTTP header values for the current request, keyed by header name
`headerValues`	A `Map` of `String` arrays containing all the header values for HTTP headers in the current request, keyed by header name
`initParam`	A `Map` of the context initialization parameters for this web application
`param`	A `Map` of the request parameters for this request, keyed by parameter name
`paramValues`	A `Map` of `String` arrays containing all the parameter values for request parameters in the current request, keyed by parameter name
`requestScope`	A `Map` of the request attributes for this request, keyed by attribute name
`sessionScope`	A `Map` of the session attributes for this request, keyed by attribute name
`view`	The root `UIComponent` in the current component tree stored in the `FacesRequest` for this request