JSP 标准标签库（JSTL）

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JSP标准标签库（JSTL）是一个JSP标签集合，它封装了JSP应用的通用核心功能。
JSTL支持通用的、结构化的任务，比如迭代，条件判断，XML文档操作，国际化标签，SQL标签。除了这些，它还提供了一个框架来使用集成JSTL的自定义标签。

获取请求参数中的值使用${param.username}

JSTL taglib 支持的jar包地址：http://tomcat.apache.org/download-taglibs.cgi

1. 简单的web例子

0.需要的jar包

taglibs-standard-compat-1.2.5.jartaglibs-standard-impl-1.2.5.jartaglibs-standard-jstlel-1.2.5.jartaglibs-standard-spec-1.2.5.jar

1.工程预览
这里写图片描述
2.Viewer层的jsp代码
WebContent/01/01.jsp:

<%@ page language="java" contentType="text/html; charset=UTF-8"    pageEncoding="UTF-8"%><!-- 导入JSTL的标签库 --><%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %><!-- 不允许忽略EL表达式 --><%@ page isELIgnored="false"%><!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>    <%pageContext.setAttribute("username", "<h1>张三</h1>"); %>    ${hello }<br />    ${param.hello}<br />    ${username }<br />    <c:out value="${username}" escapeXml="true"></c:out><br/>    <c:out value="${username}" escapeXml="false"></c:out><br/>    <c:out value="${username1 }" default="<font color='red'>查无此人</font>" escapeXml="false"></c:out><br /></body></html>

结果：
这里写图片描述
WebContent/WEB-INF/01/user.jsp:

<%@ page language="java" contentType="text/html; charset=UTF-8"    pageEncoding="UTF-8"%><%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %><%@ page isELIgnored="false" %><!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>user.jsp</title><style type="text/css">    table{        border-right: 1px solid #000;        border-bottom: 1px solid #000;    }    table td{        border-left: 1px solid #000;        border-top: 1px solid #000;        padding: 4px;    }</style></head><body>    <c:if test="${empty aa}">no "aa" property!</c:if>    <c:if test="${not empty user}">have "user" property</c:if> <br />    ${user.nickname },${user.age }<br/>    <c:if test="${user.age lt 18}">未成年</c:if><br />    <c:choose>        <c:when test="${user.age eq 18}">18 year</c:when>        <c:when test="${user.age lt 18}">nonage</c:when>        <c:otherwise>adult</c:otherwise>    </c:choose>    <table align="center" border="1" width="900" cellpadding="0" cellspacing="0">        <thead>            <tr><td>用户名</td><td>昵称</td><td>年龄</td></tr>        </thead>        <tbody>            <c:forEach var="u" items="${userList}" begin="0" end="4" step="1" varStatus ="cur">                <tr <c:if test="${cur.index%2==0}">style="background:#ff0;color:#45f;"</c:if>>                    <td>${u.name}</td><td>${u.nickname}--${cur.index}</td><td>${u.age}</td>                </tr>            </c:forEach>        </tbody>    </table></body></html>

结果：
这里写图片描述
3.controller层[servlet基于Annotation]
HelloServlet.java：

package com.my.mvc.servlet;import java.io.IOException;import javax.servlet.RequestDispatcher;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;@WebServlet("/hello")public class HelloServlet extends HttpServlet {    private static final long serialVersionUID = 3997354772023831828L;    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        System.out.println("HelloServlet doGet");        request.setAttribute("hello", "world!");        //客户端跳转//      request.getSession().setAttribute("hello", "world");//      response.sendRedirect(request.getContextPath()+"/01/01.jsp");        //服务器端跳转        //dispatcher 会自动加上 request.getContextPath()路径        RequestDispatcher dispatcher= request.getRequestDispatcher("/01/01.jsp");        dispatcher.forward(request, response);//      response.getWriter().append("Served at: ").append(request.getContextPath());    }    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        doGet(request, response);    }}

UserServlet.java：

package com.my.mvc.servlet;import java.io.IOException;import java.util.ArrayList;import java.util.List;import javax.servlet.RequestDispatcher;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.my.mvc.model.User;@WebServlet("/user.do")public class UserServlet extends HttpServlet {    private static final long serialVersionUID = 8293399267378109285L;    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        System.out.println("doGet");        User user=new User("zs", "张三", 14);        req.setAttribute("user", user);        List<User> userList=new ArrayList<>();        for(int i=0;i<5;++i) {            userList.add(new User("wukong", "悟空"+(i==0? "":""+i), 500));        }        req.setAttribute("userList", userList);        RequestDispatcher requestDispatcher=req.getRequestDispatcher("/WEB-INF/01/user.jsp");        requestDispatcher.forward(req, resp);        System.out.println(user);    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        System.out.println("doPost");        this.doGet(req, resp);    }}

model层：
User.java：

package com.my.mvc.model;public class User {    private String name;    private String nickname;    private int age;    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public String getNickname() {        return nickname;    }    public void setNickname(String nickname) {        this.nickname = nickname;    }    public User(String name, String nickname, int age) {        super();        this.name = name;        this.nickname = nickname;        this.age = age;    }    public User() {    }    @Override    public String toString() {        return "User [name=" + name + ", nickname=" + nickname + ", age=" + age + "]";    }}

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