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JSP Custom tags with example – JSP Tutorial

2015-09-01 13:39 676 查看

User-defined tags are known as custom tags. In this tutorial we will see how to create a custom tag and use it in JSP.

To create a custom tag we need three things:

1) Tag handler class: In this class we specify what our custom tag will do when it is used in a JSP page.

2) TLD file: Tag descriptor file where we will specify our tag name, tag handler class and tag attributes.

3) JSP page: A JSP page where we will be using our custom tag.

Example:

In the below example we are creating a custom tag

MyMsg

which will display the message “

This is my own custom tag

” when used in a JSP page.

Tag handler class:

A tag handler class should implement

Tag

IterationTag

BodyTag

interface or it can also extend

TagSupport

BodyTagSupport

SimpleTagSupport

class. All the classes that support custom tags are present inside

javax.servlet.jsp.tagext

. In the below we are extending the class

SimpleTagSupport

Details.java

package beginnersbook.com;
import javax.servlet.jsp.tagext.*;
import javax.servlet.jsp.*;
import java.io.*;
public class Details extends SimpleTagSupport {
public void doTag() throws JspException, IOException {
/*This is just to display a message, when
* we will use our custom tag. This message
* would be displayed
*/
JspWriter out = getJspContext().getOut();
out.println("This is my own custom tag");
}
}

TLD File

This file should present at the location:

Project Name/WebContent/WEB-INF/

and it should have a

.tld

extension.

Note:

<name

> tag: custom tag name. In this example we have given it as

MyMsg

<tag-class>

tag: Fully qualified class name. Our tag handler class

Details.java

is in package

beginnersbook.com

so we have given the value as

beginnersbook.com.Details

.

message.tld

<taglib>
<tlib-version>1.0</tlib-version>
<jsp-version>2.0</jsp-version>
<short-name>My Custom Tag</short-name>
<tag>
<name>MyMsg</name>
<tag-class>beginnersbook.com.Details</tag-class>
<body-content>empty</body-content>
</tag>
</taglib>

Using custom tag in JSP:

Above we have created a custom tag named

MyMsg

. Here we will be using it.

Note:

taglib

directive should have the TLD file path in

uri

field. Above we have created the

message.tld

file so we have given the path of that file.

Choose any prefix and specify it in

taglib

directive’s

prefix

field. Here we have specified it as

myprefix

.

Custom tag is called like this:

<prefix:tagName/>

. Our prefix is myprefix and tag name is

MyMsg

so we have called it as

<myprefix:MyMsg/>

in the below JSP page.

<%@ taglib prefix="myprefix" uri="WEB-INF/message.tld"%>
<html>
<head>
<title>Custom Tags in JSP Example</title>
</head>
<body>
<myprefix:MyMsg/>
</body>
</html>

Output:

This is my own custom tag

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