Tags in JSP

By: aathishankaran Printer Friendly Format

The important syntax elements of JSP are tags. The JSP tags do not use <%, but just the < character.

A JSP tag is somewhat like an HTML tag. JSP tags can have a "start tag", a "tag body" and an "end tag". The start and end tag both use the tag name, enclosed in < and > characters. The end starts with a / character after the < character. The tag names have an embedded colon character : in them, the part before the colon describes the type of the tag.

For instance:

<some:tag>
body
</some:tag>

If the tag does not require a body, the start and end can be conveniently merged together, as

<some:tag/>

Here by closing the start tag with a /> instead of > character, we are ending the tag immediately, and without a body. (This syntax convention is the the same as XML.)

Tags can be of two types: loaded from an external tag library, or predefined tags. Predefined tags start with jsp: characters. For instance, jsp:include is a predefined tag that is used to include other pages.

We have already seen the include directive in previous examples. jsp:include is similar. But instead of loading the text of the included file in the original file, it actually calls the included target at run-time (the way a browser would call the included target. In practice, this is actually a simulated request rather than a full round-trip between the browser and the server).

Following is an example of jsp:include usage

<HTML>


<BODY>


Going to include hello.jsp...<BR>


<jsp:include page="hello.jsp"/>


</BODY>


</HTML>

Try it and see what you get. Now change the "jsp:include" to "jsp:forward" and see what is the difference. These two predefined tags are frequently very useful.

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