el表达式和标签库的简单使用！！！

备工作1：tomcat10.1.13版本，可去官网下载，不会下载的童靴看过来：如何正确下载tomcat？？？_明天更新的博客-CSDN博客

 准备工作2：添加架包（需要三个架包）

jstl架包，下载地址：有道云笔记

 准备好这三个架包后，创建一个普通的JavaWeb项目。

不太了解创建步骤的看这里：idea如何建立web项目？？？_明天更新的博客-CSDN博客

 1.搭建servlet环境

详细步骤：servlet初体验之环境搭建！！！_明天更新的博客-CSDN博客

2.if标签库的使用

Java代码（Servlet）：

/*
 * Copyright (c) 2020, 2023,  All rights reserved.
 *
 */
package cn;

import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

/**
 * 
Project: servlet-web-jstl - UserListServlet
 * 
Powered by scl On 2023-09-01 20:52:50
 * 
描述：

 *
 * @author 孙臣龙 [[email protected]]
 * @version 1.0
 * @since 17
 */
@WebServlet("/userListServlet")
public class UserListServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html;charset=utf-8");
        req.setCharacterEncoding("utf-8");
        String age = req.getParameter("age");
        req.setAttribute("age",age);
        req.getRequestDispatcher("user.jsp").forward(req,resp);


    }
}

jsp代码：因为要使用到标签库，一定要加上这个：

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>    适用tomcat10以上的版本

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>


    


${age}

  
年龄大于18岁


  
年龄小于18岁


  
年龄为18岁，恭喜你以成年！！

结果显示：

3.foreach标签库的使用

Java代码（user类）：

/*
 * Copyright (c) 2020, 2023,  All rights reserved.
 *
 */
package cn;

/**
 * 
Project: servlet-web-jstl - UserEntity
 * 
Powered by scl On 2023-09-02 10:47:58
 * 
描述：

 *
 * @author 孙臣龙 [[email protected]]
 * @version 1.0
 * @since 17
 */
public class UserEntity {
    /**
     * 用户名称
     */
    private String username;
    /**
     * 用户年龄
     */
    private Integer age;
    /**
     * 状态 0：冻结状态   1：为冻结
     */
    private Integer start;

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Integer getStart() {
        return start;
    }

    public void setStart(Integer start) {
        this.start = start;
    }

    public UserEntity(String username, Integer age, Integer start) {
        this.username = username;
        this.age = age;
        this.start = start;
    }

    public UserEntity() {
    }
}

Java代码（servlet）：

/*
 * Copyright (c) 2020, 2023,  All rights reserved.
 *
 */
package cn;

import com.sun.net.httpserver.HttpServer;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

/**
 * 
Project: servlet-web-jstl - UserListServletFor
 * 
Powered by scl On 2023-09-02 10:45:16
 * 
描述：

 *
 * @author 孙臣龙 [[email protected]]
 * @version 1.0
 * @since 17
 */
@WebServlet("/userListServletFor")
public class UserListServletFor extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        List list=new ArrayList<>();
        list.add(new UserEntity("小明",14,0));
        list.add(new UserEntity("小红",22,1));
        list.add(new UserEntity("小绿",44,1));
        list.add(new UserEntity("小王",18,0));
        req.setAttribute("userList",list);
        req.getRequestDispatcher("userList.jsp").forward(req,resp);
    }
}

jsp页面：

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%--
  Created by IntelliJ IDEA.
  User: admin
  Date: 2023/9/2
  Time: 10:53
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>


    



        

    

        
序号
        
名称
        
年龄
        
冻结
        
操作
    
    

            
${m.index+1}
            
${user.username}
            
${user.age}
            
冻结状态未冻结
            
修改    删除
        
    

结果显示：