本节讲述自定义标签的用法。

1、环境约束

idea2018.1.5
maven-3.0.5
jdk-8u162-windows-x64
servlet3.0

2、前提约束

完成servlet的三种实现方式，假设该项目的名称为为servlet-jstl
在pom.xml中加入依赖

        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>

在servlet-test/src/main/java文件夹下创建net.wanho.tag包
在net.wanho.tag包下面创建ForEach.java

package net.wanho.tag;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.SimpleTagSupport;
import java.io.IOException;
import java.util.Collection;

public class ForEach extends SimpleTagSupport {
    private Collection<?> items;

    public void setItems(Collection<?> items) {
        this.items = items;
    }

    private String var;

    public void setVar(String var) {
        this.var = var;
    }

    @Override
    public void doTag() throws JspException, IOException {
        if (items != null) {
            for (Object obj : items) {
                getJspContext().setAttribute(var, obj);
                getJspBody().invoke(null);
            }
        }
    }
}

在net.wanho.tag包下面创建Student.java

package net.wanho.tag;

import java.io.Serializable;

public class Student implements Serializable {
    private int id;
    private String name;

    public Student(int id, String name) {
        this.id = id;
        this.name = name;
    }

    public Student() {
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

在servlet-test/src/main/webapp/WEB-INF文件夹下创建my.tld

<?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 http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"
        version="2.0">
    <description>MyTag 1.2 core library</description>
    <display-name>MyTag core</display-name>
    <tlib-version>1.2</tlib-version>
    <short-name>mytag</short-name>
    <uri>http://tag.com/mytag/core</uri>
    <tag>
        <name>forEach</name>
        <tag-class>net.wanho.tag.ForEach</tag-class>
        <body-content>scriptless</body-content>
        <attribute>
            <name>items</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>var</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
    </tag>
</taglib>

在servlet-test/src/main/webapp文件夹下创建tag.jsp

<%@ page import="net.wanho.tag.Student" %>
<%@ page import="java.util.ArrayList" %>
<%@ page import="java.util.List" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="tag" uri="http://tag.com/mytag/core" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<%
    List<Student> tg = new ArrayList<Student>();
    tg.add(new Student(1, "AAA"));
    tg.add(new Student(2, "BBB"));
    tg.add(new Student(3, "CCC"));
    tg.add(new Student(4, "DDD"));
    request.setAttribute("tg", tg);
%>

<!-- 使用标签库foreach -->
<c:forEach items="${requestScope.tg}" var="abc">
    ${abc.id}--${abc.name}<br>
</c:forEach>

<!-- 使用自定义标签foreach -->
<tag:forEach items="${requestScope.tg }" var="abc">
    ${abc.id}--${abc.name}<br>
</tag:forEach>
</body>
</html>

启动测试，浏览器访问 http://localhost:8088/tag.jsp

以上就是自定义标签的定义和使用。

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05 自定义标签

1、环境约束

2、前提约束

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