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What is the function of the JSP Taglib directive?

2022-08-02 00:18:00 【qq_25073223】

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JSP TaglibWhat is the function of the command？

下文讲述JSP中TaglibA brief description of the function of the command,如下所示:

Taglib指令的功能:
  Defines a tag library and prefixes for its custom tags 一个自定义的tagA label is a user-defined typeJSP标记 when one contains custom tag标签的JSP页面被jsp引擎编译成servlet时 此时tag标签被转化成了对一个称为tagHandles operations performed by objects of a class 当JSP页面被jsp引擎转化为servlet后,实际上tagLabels are converted into pairstag处理类的操作

Taglib指令的语法

<%@ taglib uri="" prefix="c"%>
     prefix:is a tag library alias 
     taglib之uri:引入jsp的标签库

Taglib子元素

ElementDescription
tlib-versionTag库的版本
jsp-versionTag库所需要的jsp的版本
short-name：助记符,tag的一个别名（可选）
uriUsed to determine a uniquetag库
display-namebe visualized（诸如Jbuilder）The name used to display（可选）
small-iconbe visualized（诸如Jbuilder）Small icon to display（可选）
large-iconbe visualized（诸如Jbuilder）Large icons for display（可选）
description对tag库的描述（可选）
listener一个tagA library may define some classes as its event listener classes,这些类在TLD中被称为listener 元素,jspThe server will instantiate these listener classes,并且注册它们.ListenerOne of the elements is calledlistener-class的子元素,The value of this element must be the full class name of the listener class
tagtag元素在tagThe library needs to indicate its name、类名、脚本变量、tag的属性
The value of the script variable can be directly inTLDdefined in or passedtagAdditional information for the class to obtain
Each attribute describes whether the attribute can be omitted,Whether its value can be passed<%= …%>
这样的JSPgrammar to get,and the type of the property tag子元素如下：
name：Unique element name
tag-class：Tag标签对应的tag处理类
tei-class：javax.servlet.jsp.tagext.TagExtraInfo的子类,Used to express script variables（可选）
body-content：Tag标签body的类型
display-name：be visualized（诸如Jbuilder）The name used to display（可选）
small-icon：be visualized（诸如Jbuilder）Small icon to display（可选）
large-icon：be visualized（诸如Jbuilder）Large icons for display（可选）
description：此tag标签的描述
variable：Provides information about script variables（同tei-class）(可选)
attribute：Tag标签的属性名

Taglib引入方式

jsp文件:

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>  
<%@ taglib prefix="c" uri="myjstl" %>  
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">  
<html>  
<head>  
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">  
    <title>Insert title here</title>  
</head>  
<body>  
    <c:out value="${param.username}"/>  
</body>  
</html>


web.xml

<web-app id="WebApp_ID" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">  
                ...  
    <jsp-config>  
       <taglib>  
           <taglib-uri>myjstl</taglib-uri>  
           <taglib-location>/WEB-INF/tld/c.tld</taglib-location>  
       </taglib>  
    </jsp-config>  
                ...  
</web-app>

Standard definition labels

jsp Taglib指令tld例子

<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>collection</title>
</head>
<body>
<c:forEach var="l" items="${list}">
<table>
    <th>
        <td>编号</td>
        <td>姓名</td>
        <td>年龄</td>
        <td>时间</td>
    </th>
    <tr>
        <td>${l.id}</td>
        <td><a href="*****${l.id}">${l.name}</a></td>
        <td>${l.age}</td>
        <td><a href="*****${l.url}">编辑</a><a href="*****${l.url}">删除</a></td>
    </tr>
</table>
</c:forEach>
</body>
</html>

开发自定义标签

开发自定义标签,The following methods are required:
    步骤一：
	必须继承一个父类：javax.servlet.jsp.tagext.SimpleTagSupport 
    每个属性都有对应的getter和setter方法.
    重写doTag()或者doStartTag()或doEndTag()方法方法
	 This method is responsible for generating the page content.

public class TestTag extends TagSupport {
    private static final long serialVersionUID = -3382691015235241708L;
    @Override
    public int doEndTag() throws JspException {
        try {
            pageContext.getOut().write("MyTag");
            return super.doEndTag();
        } catch(JspException e) {
            e.printStackTrace();
            return 0;
        } catch(IOException e) {
            e.printStackTrace();
            return 0;
        }
    }
    @Override
    public int doStartTag() {
        try {
            pageContext.getOut().write("MyTag");
            return super.doStartTag();
        } catch(JspException e) {
            e.printStackTrace();
            return 0;
        } catch(IOException e) {
            e.printStackTrace();
            return 0;
        }
    }
}

 
步骤二：
  建立一个*.tld文件,每个*.tldThe file corresponds to a tag library,Each tag library corresponds to multiple tags
注意事项:
   TLD(Tag Library Definition)That is, the tag library definition
   文件的后缀是tld
    每个TLDThe file corresponds to a tag library
    A tag library can contain multiple tags
    TLDThe file is also known as a tag library definition file
  The root element of the tag library definition file is taglib
    它可以包含多个tag子元素
      每个tagChild elements all define a label 

 
<?xml version="1.0" encoding="utf-8"?>
<taglib xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee web-jsptaglibrary_2_0.xsd" version="2.0"> 
  <tlib-version>1.0</tlib-version>  
  <short-name>myhelloworld</short-name>  
  <!-- 定义该标签库的URI Must be added but can be empty-->  
  <uri/>  
  <!-- 定义第一个标签 -->  
  <tag> 
    <!-- 定义标签名 -->  
    <name>thisTag</name>  
    <!-- 定义标签处理类 -->  
    <tag-class>com.java265.taglib.TestTag</tag-class>  
    <!-- 定义标签体为空 -->  
    <body-content>empty</body-content> 
  </tag> 
</taglib>
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https://yzsam.com/2022/214/202208020000566121.html

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