Defining the Custom Component Tag in a Tag Library Descriptor

To define a tag, you declare it in a TLD. The web container uses the TLD to validate the tag. The set of tags that are part of the HTML render kit are defined in the html_basic TLD.

The custom tags area and map are defined in bookstore.tld. The bookstore.tld file defines tags for all the custom components and the custom validator tag described in Creating a Custom Tag (page 406).

All tag definitions must be nested inside the taglib element in the TLD. Each tag is defined by a tag element. Here is part of the tag definition of the map tag:

<tag>
  <name>map</name>
  <tag-class>taglib.MapTag</tag-class>
  <attribute>
    <name>binding</name>
    <required>false</required>
    <deferred-value>
      <type>
        javax.faces.component.UIComponent
      </type>
    </deferred-value>
  </attribute>
  <attribute>
    <name>current</name>
    <required>false</required>
    <deferred-value>
      <type>
        java.lang.String
      </type>
    </deferred-value>
  </attribute>
  ...
  <attribute>
    <name>actionListener</name>
    <required>false</required>
    <deferred-method>
      <method-signature>
        void actionListener(javax.faces.event.ActionEvent)
      </method-signature>
    </deferred-method>
    <type>String</type>
  </attribute>
  ...
</tag>

At a minimum, each tag must have a name (the name of the tag) and a tag-class attribute, which specifies the fully-qualified class name of the tag handler.

Each attribute element defines one of the tag attributes. As described in Defining a Tag Attribute Type (page 119), the attribute element must define what kind of value the attribute accepts, which for JavaServer Faces tags is either a deferred value expression or a method expression.

To specify that an attribute accepts a deferred value expression, you define the type that the corresponding component property accepts using a type element nested inside of a deferred-value element, as shown for the binding and current attribute definitions in the preceding code snippet.

To specify that an attribute accepts a method expression, you define the signature of the method that expression references using a method-signature element nested inside a deferred-method element, as shown by the actionListener attribute definition in the preceding code snippet. The actual name of the method is ignored by the runtime.