Overview of JSP Syntax Elements
First, to make things more clear, here is a short overview of JSP syntax elements:
- Directives: These convey information regarding the JSP page as a
- Scripting elements: These are Java coding elements such as
declarations, expressions, scriptlets, and comments.
- Objects and scopes: JSP objects can be created either explicitly or
implicitly and are accessible within a given scope, such as from
anywhere in the JSP page or the session.
- Actions: These create objects or affect the output stream in the JSP
response (or both).
How content is included in JSP
There are several mechanisms for reusing content in a JSP file.
The following 4 mechanisms to include content in JSP can be categorized as direct reuse:
(for the first 3 mechanisms quoting from “Head First Servlets and JSP”)
1) The include directive:
<%@ include file="header.html" %>
Static: adds the content from the value of the file attribute to the current page at translation time. The directive was
originally intended for static layout templates, like HTML headers.
<jsp:include page="header.jsp" />
Dynamic: adds the content from the value of the page attribute to the current page at request time. Was intended more for dynamic
content coming from JSPs.
<c:import url=”http://www.example.com/foo/bar.html” />
Dynamic: adds the content from the value of the URL attribute to the current page, at request time. It works a lot like
<jsp:include>, but it’s more powerful and flexible: unlike the
other two includes, the
<c:import>URL can be from outside the
4) Preludes and codas:
Static: preludes and codas can be applied only to the beginnings and ends of pages.
You can implicitly include preludes (also called headers) and codas
(also called footers) for a group of JSP pages by adding
<include-coda>elements respectively within
<jsp-property-group>element in the Web application web.xml deployment descriptor.
Tag File is an indirect method of content reuse, the way of encapsulating reusable content.
A Tag File is a source file that contains a fragment of JSP code that is reusable as a custom tag.
The PURPOSE of includes and Tag Files is different.
Tag file (a concept introduced with JSP 2.0) is one of the options for creating custom tags. It’s a faster and easier way to build custom tags.
Custom tags, also known as tag extensions, are JSP elements that allow custom logic and output provided by other Java components to be inserted into JSP pages. The logic provided through a custom tag is implemented by a Java object known as a tag handler.
Some examples of tasks that can be performed by custom tags include operating on implicit objects, processing forms, accessing databases and other enterprise services such as email and directories, and implementing flow control.
Regarding your Edit
Maybe in your example (in your “Edit” paragraph), there is no difference between using direct include and a Tag File. But custom tags have a rich set of features. They can
Be customized by means of attributes passed from the calling page.
Pass variables back to the calling page.
Access all the objects available to JSP pages.
Communicate with each other. You can create and initialize a JavaBeans component, create a public EL variable that refers to that bean in one tag, and then use the bean in another tag.
Be nested within one another and communicate by means of private variables.
Also read this from “Pro JSP 2”: Understanding JSP Custom Tags.
JSP tricks to make templating
Very informative and easy to understand tutorial from coreservlet.com with beautiful
explanations that include
<jsp:include> VS. <%@ include %>
Including Files and Applets in JSP
Another nice tutorial from coreservlets.com related to tag libraries and
Creating Custom JSP Tag Libraries: The
The official Java EE 5 Tutorial with examples:
Encapsulating Reusable Content
This page from the official Java EE 5 tutorial should give you even
Reusing Content in JSP
This excerpt from the book “Pro JSP 2” also discuses why do you need
a Tag File instead of using static include:
Reusing Content with Tag
Very useful guide right from the Oracle documentation:
Static Includes Versus Dynamic Includes
Use the right tools for each task.
Use Tag Files as a quick and easy way of creating custom tags that can help you encapsulate reusable content.
As for the including content in JSP (quote from here):
- Use the include directive if the file changes rarely. It’s the fastest mechanism. If your container doesn’t automatically detect changes, you can force the changes to take effect by deleting the main page class file.
- Use the include action only for content that changes often, and if which page to include cannot be decided until the main page is requested.