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What is the use of jsp custom tags

(*-*)浩Original: 2019-05-16 10:55:483703browse

Custom JSP tags are usually for reuse. For example, the same function does not need to be written in the same code on different pages to facilitate the maintenance of page code; custom tags are user-defined JSP language elements that create custom The syntax for defining tags is "".

Custom tags are user-defined JSP language elements. When a JSP page contains a custom tag that is converted into a servlet, the tag is converted into operations on an object called a tag handler, which are operations that the Web container calls when the servlet is executed. Custom JSP tags are usually for reuse. For example, the same function does not need to be written in the same code on different pages, which facilitates the maintenance of page code.

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JSP tag extension allows you to create new tags and insert them directly into a JSP page. Simple Tag Handlers were introduced in the JSP 2.0 specification to write these custom tags.

You can inherit the SimpleTagSupport class and override the doTag() method to develop the simplest custom tag.

Create the "Hello" tag

Next, we want to create a custom tag called , the tag format is:

<span style='font-family: "Microsoft Yahei", "Hiragino Sans GB", Helvetica, "Helvetica Neue", å¾®è½¯é›…é»‘, Tahoma, Arial, sans-serif;'><ex:Hello /></span>    <br>

To create custom JSP tags, you must first create the Java class that handles the tags. So, let us create a HelloTag class as follows:

package com.runoob;

import javax.servlet.jsp.tagext.*;
import javax.servlet.jsp.*;
import java.io.*;

public class HelloTag extends SimpleTagSupport {

 public void doTag() throws JspException, IOException {
   JspWriter out = getJspContext().getOut();
   out.println("Hello Custom Tag!");
 }
}

The following code overrides the doTag() method, which uses the getJspContext() method to obtain the current JspContext object and replace "Hello Custom Tag!" is passed to the JspWriter object.

Compile the above class and copy it to the environment variable CLASSPATH directory. Finally, create the following tag library: webapps\ROOT\WEB-INF\custom.tld.

<taglib>
 <tlib-version>1.0</tlib-version>
 <jsp-version>2.0</jsp-version>
 <short-name>Example TLD</short-name>
 <tag>
   <name>Hello</name>
   <tag-class>com.runoob.HelloTag</tag-class>
   <body-content>empty</body-content>
 </tag>
</taglib>

Next, we can use the Hello tag in the JSP file:

<%@ taglib prefix="ex" uri="WEB-INF/custom.tld"%><html> <head>   <title>A sample custom tag</title> </head> <body>   <ex:Hello/> </body></html>

The output result of the above program is:

Hello Custom Tag!

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