Declaring Tag Variables in Tag Files

Tag attributes are used to customize tag behavior much as parameters are used to customize the behavior of object methods. In fact, using tag attributes and EL variables, it is possible to emulate various types of parameters: IN, OUT, and nested.
To emulate IN parameters, use tag attributes. A tag attribute is communicated between the calling page and the tag file when the tag is invoked. No further communication occurs between the calling page and the tag file.

description(optional) An optional description of this variable. Defaults to no description.
name-given | name-from-attributeDefines an EL variable to be used in the page invoking this tag. Either name-given or name-from-attribute must be specified. If name-given is specified, the value is the name of the variable. If name-from-attribute is specified, the value is the name of an attribute whose (translation-time) value at the start of the tag invocation will give the name of the variable.
Translation errors arise in the following circumstances: 1. Specifying neither name-given nor name-from-attribute or both.
2. If two variable directives have the same name-given.
3. If the value of a name-given attribute of a variable directive is equal to the value of a name attribute of an attribute directive or the value of a dynamic-attributes attribute of a tag directive.
aliasDefines a variable, local to the tag file, to hold the value of the EL variable. The container will synchronize this value with the variable whose name is given in name-from-attribute.
Required when name-from-attribute is specified. A translation error results if used without name-from-attribute.
A translation error results if the value of alias is the same as the value of a name attribute of an attribute directive or the name-given attribute of a variable directive.
variable-class(optional) The name of the class of the variable. The default is java.lang.String.
declare(optional) Whether or not the variable is declared. True is the default.
scope(optional) The scope of the variable. Can be either AT_BEGIN, AT_END, or NESTED. Defaults to NESTED.

To emulate OUT or nested parameters, use EL variables. The variable is not initialized by the calling page but instead is set by the tag file. Each type of parameter is synchronized with the calling page at various points according to the scope of the variable. See Variable Synchronization for details.

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