Displaying a Formatted Message with the outputFormat Tag

The outputFormat tag allows a page author to display concatenated messages as a MessageFormat pattern, as described in the API documentation for java.text.MessageFormat (see http://java.sun.com/javase/6/docs/api/java/text/MessageFormat.html). Here is an example of an outputFormat tag from the bookshowcart.jsp page of the Duke’s Bookstore application:

<h:outputFormat value="#{bundle.CartItemCount}">
    <f:param value="#{cart.numberOfItems}"/>
</h:outputFormat>

The value attribute specifies the MessageFormat pattern. The param tag specifies the substitution parameters for the message.

In the example outputFormat tag, the value for the parameter maps to the number of items in the shopping cart. When the message is displayed on the page, the number of items in the cart replaces the {0} in the message corresponding to the CartItemCount key in the bundle resource bundle:

Your shopping cart contains " + "{0,choice,0#no items|1#one item|1< {0} items

This message represents three possibilities:

• Your shopping cart contains no items.

• Your shopping cart contains one item.

• Your shopping cart contains {0} items.

The value of the parameter replaces the {0} from the message in the sentence in the third bullet. This is an example of a value-expression-enabled tag attribute accepting a complex EL expression.

An outputFormat tag can include more than one param tag for those messages that have more than one parameter that must be concatenated into the message. If you have more than one parameter for one message, make sure that you put the param tags in the proper order so that the data is inserted in the correct place in the message.

A page author can also hard code the data to be substituted in the message by using a literal value with the value attribute on the param tag.