It seems that there are two methods for templating with JSP. Including files with one of these statements
<%@ include file="foo.html" %>
<jsp:include page="foo.html" />
or using JSP tag files
// Save this as mytag.tag
<%@ tag description="Description" pageEncoding="UTF-8"%>
<html>
<head>
</head>
<body>
<jsp:doBody/>
</body>
</html>
And in another JSP page call it with
<%@ taglib prefix="t" tagdir="/WEB-INF/tags" %>
<t:mytag>
<h1>Hello World</h1>
</t:mytag>
So which method should I use? Is one now considered deprecated or are they both valid and cover different use cases?
Edit
Isn't using this tag file the same as using an include?
// Save this as product.tag
<%@ tag description="Product templage" pageEncoding="UTF-8"%>
<%@ tag import="com.myapp.Product" %>
<%@ attribute name="product" required="true" type="com.myapp.Product"%>
Product name: ${product.name} <br/>
Quantity: ${product.quantity} <br/>
And call it on another JSP with
<%@ taglib prefix="t" tagdir="/WEB-INF/tags" %>
<t:product>
<c:forEach items="${cart.products}" var="product">
<t:product product="${product}"/>
</c:forEach>
</t:product>
That seems to me to be the very same as using an include and passing parameters to it. So are Tag Files the same as includes?
Main advantage of
<jsp:include />
over<%@ include >
is:<jsp:include />
allows to pass parameterswhich is not possible in
<%@include file="somefile.jsp" %>
All three template options -
<%@include>
,<jsp:include>
and<%@tag>
are valid, and all three cover different use cases.With
<@include>
, the JSP parser in-lines the content of the included file into the JSP before compilation (similar to a C#include
). You'd use this option with simple, static content: for example, if you wanted to include header, footer, or navigation elements into every page in your web-app. The included content becomes part of the compiled JSP and there's no extra cost at runtime.<jsp:include>
(and JSTL's<c:import>
, which is similar and even more powerful) are best suited to dynamic content. Use these when you need to include content from another URL, local or remote; when the resource you're including is itself dynamic; or when the included content uses variables or bean definitions that conflict with the including page.<c:import>
also allows you to store the included text in a variable, which you can further manipulate or reuse. Both these incur an additional runtime cost for the dispatch: this is minimal, but you need to be aware that the dynamic include is not "free".Use tag files when you want to create reusable user interface components. If you have a List of Widgets, say, and you want to iterate over the Widgets and display properties of each (in a table, or in a form), you'd create a tag. Tags can take arguments, using
<%@tag attribute>
and these arguments can be either mandatory or optional - somewhat like method parameters.Tag files are a simpler, JSP-based mechanism of writing tag libraries, which (pre JSP 2.0) you had to write using Java code. It's a lot cleaner to write JSP tag files when there's a lot of rendering to do in the tag: you don't need to mix Java and HTML code as you'd have to do if you wrote your tags in Java.
Java Revisited
Possible Duplicate Question
<@include>
- The directive tag instructs the JSP compiler to merge contents of the included file into the JSP before creating the generated servlet code. It is the equivalent to cutting and pasting the text from your include page right into your JSP.<jsp:include>
- The JSP Action tag on the other hand instructs the container to pause the execution of this page, go run the included page, and merge the output from that page into the output from this page.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")
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), 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.
Useful reading.
Difference between include directive and include action in JSP
JSP tricks to make templating easier
Very informative and easy to understand tutorial from coreservlet.com with beautiful explanations that include
<jsp:include> VS. <%@ include %>
comparison table:Including Files and Applets in JSP Pages
Another nice tutorial from coreservlets.com related to tag libraries and tag files:
Creating Custom JSP Tag Libraries: The Basics
The official Java EE 5 Tutorial with examples:
Encapsulating Reusable Content Using Tag Files.
This page from the official Java EE 5 tutorial should give you even more understanding:
Reusing Content in JSP Pages.
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 Files
Conclusion
Use the right instruments for the concrete task.
Use Tag Files as a quick and easy way of creating custom tags.
As for the including content in JSP (quote from here):