Declaring Tag Attributes in Tag Files (The Java EE 5 Tutorial)

The Java EE 5 Tutorial

Declaring Tag Attributes in Tag Files

To declare the attributes of a custom tag defined in a tag file, you use the attribute directive. A TLD has an analogous attribute element (see Declaring Tag Attributes for Tag Handlers). Table 8–3 lists the attribute directive attributes.

Table 8–3 attribute Directive Attributes


Attribute	Description
`description`	(optional) Description of the attribute. Defaults to no description.
`name`	The unique name of the attribute being declared. A translation error results if more than one `attribute` directive appears in the same translation unit with the same `name`. A translation error results if the value of a `name` attribute of an `attribute` directive is equal to the value of the `dynamic-attributes` attribute of a `tag` directive or the value of a `name-given` attribute of a `variable` directive.
`required`	(optional) Whether this attribute is required (`true`) or optional (`false`). Defaults to `false`.
`rtexprvalue`	(optional) Whether the attribute’s value can be dynamically calculated at runtime by an expression. Defaults to `true`. When this element is set to `true` and the attribute definition also includes either a `deferred-value` or `deferred-method` element then the attribute accepts both dynamic and deferred expressions.
`type`	(optional) The runtime type of the attribute’s value. Defaults to `java.lang.String`.
`deferredValue`	(optional) Indicates whether the attribute accepts deferred value expressions. Only one of `deferredValue` or `deferredMethod` can be true. If `deferredValueType` is specified, the default for `deferredValue` is `true`. Causes a translation error if specified in a tag file with a JSP version less than 2.1.
`deferredValueType`	(optional) The type resulting from the evaluation of the attribute’s value expression. The default is `java.lang.String` if no type is specified. If both `deferredValueType` and `deferredValue` are specified, `deferredValue` must be true. If `deferredValue` is `true`, the default of `deferredValueType` is `java.lang.Object`. Causes a translation error specified in a tag file with a JSP version less than 2.1.
`deferredMethod`	(optional) Indicates whether the tag attribute accepts deferred method expressions. If `deferredMethod` and `deferredMethodSignature` are specified then `deferredMethod` must be true. The default of `deferredMethod` is true if `deferredMethodSignature` is specified, otherwise the default of `deferredMethod` is false. The presence of a `deferred-method` element in an attribute definition precludes the inclusion of a `deferred-value` element. Causes a translation error if specified in a tag file with a JSP version less than 2.1.
`deferredMethodSignature`	(optional) The signature of the method to be invoked by the expression defined by the accompanying `deferredMethod` attribute. If `deferredMethod` is true and this attribute is not specified, the method signature defaults to `void methodName()`. Causes a translation error if specified in a tag file with a JSP version less than 2.1.
`fragment`	(optional) Whether this attribute is a fragment to be evaluated by the tag handler (`true`) or a normal attribute to be evaluated by the container before being passed to the tag handler. If this attribute is `true`: You do not specify the `rtexprvalue` attribute. The container fixes the `rtexprvalue` attribute at `true`. You do not specify the `type` attribute. The container fixes the `type` attribute at `javax.servlet.jsp.tagext.JspFragment`. Defaults to `false`.