Displaying Error Messages With the h:message and h:messages Tags

The h:message and h:messages tags are used to display error messages when conversion or validation fails. The h:message tag displays error messages related to a specific input component, whereas the h:messages tag displays the error messages for the entire page.

Here is an example h:message tag from the guessNumber application:

<h:inputText id="userNo" value="#{UserNumberBean.userNumber}">
    <f:validateLongRange minimum="0" maximum="10" />
 <h:commandButton id="submit"
         action="success" value="Submit" /><p>
<h:message
     style="color: red;
     font-family: ’New Century Schoolbook’, serif;
     font-style: oblique;
     text-decoration: overline" id="errors1" for="userNo"/>

The for attribute refers to the ID of the component that generated the error message. The error message is displayed at the same location that the h:message tag appears in the page. In this case, the error message will appear after the Submit button.

The style attribute allows you to specify the style of the text of the message. In the example in this section, the text will be red, New Century Schoolbook, serif font family, and oblique style, and a line will appear over the text. The message and messages tags support many other attributes for defining styles. For more information on these attributes, refer to the PDL documentation at http://java.sun.com/javaee/javaserverfaces/2.0/docs/pdldocs/facelets/index.html.

Another attribute supported by h:messages tag is the layout attribute. Its default value is list, which indicates that the messages are displayed in a bullet list using the HTML ul and li elements. If you set the attribute value to table, the messages will be rendered in a table using the HTML table element.

The preceding example shows a standard validator that is registered on the input component. The message tag displays the error message that is associated with this validator when the validator cannot validate the input component’s value. In general, when you register a converter or validator on a component, you are queueing the error messages associated with the converter or validator on the component. The h:message and h:messages tags display the appropriate error messages that are queued on the component when the validators or converters registered on that component fail to convert or validate the component’s value.

Standard error messages are provided with standard converters and standard validators. An application architect can override these standard messages and supply error messages for custom converters and validators by registering custom error messages with the application through the message-bundle. Creating and using custom error messages is an advanced topic covered in Java EE 6 Tutorial, Volume II: Advanced Topics.