C H A PT E R
5
Tag Extensions
This chapter describes the mechanisms for defining new actions in portable way and for 
introducing new actions into a JSP page.
5.1
Introduction
A Tag Library abstracts some functionality by defining a specialized (sub)language that 
enables a more natural use of that functionality within JSP pages. The actions introduced by 
the Tag Library can be used by the JSP page author in JSP pages explicitly, when authoring 
the page manually, or implicitly, when using an authoring tool.  Tag Libraries are particularly 
useful to authoring tools because they make intent explicit and the parameters expressed  in 
the action instance provide information to the tool.
Actions that are delivered as tag libraries are imported into a JSP page using the 
taglib
directive, and can then be used in the page using the prefix given by the directive. An action 
can create new objects that can then be passed to other actions or can be manipulated 
programmatically through an scripting element in the JSP page.
Tag libraries are portable: they can be used in any legal JSP page regardless of the scripting 
language used in that page.
The tag extension mechanism includes information to:
Execute a JSP page that uses the tag library.
Author and modify a JSP page.
Present the JSP page to the end user.
The JSP 1.1 specification mostly includes the first kind of information, plus basic 
information of the other two kinds.  Later releases of the JSP specification may provide 
additional information; in the meanwhile, vendors may use vendor specific information to 
address their needs.
 Tag Extensions
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