jsp JSTL标签详细示例（c:if与c:forEach）

JSTL标准标签库（jsp Standarded Tag Library），使用标签来取代jsp页面上的Java代码

JSTL标签库有很多，我们只学两个，if标签的替代和for循环标签的替代

JSTL快速入门（使用步骤）

1.导入坐标

    jstl
    jstl
    1.2

    taglibs
    standard
    1.1.2

2.在jsp页面页面上引入JSTL标签库

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>

3.使用

1.c:if标签相当于Java中的if else标签

（我们结合el标签来进行判断，从servlet中获取值，在jsp文件中进行判断）

实体类brand


package com.ithema.pojo;
/*
在实体类中，基本数据类型，建议使用其对应的包装类
 */
public class Brand {
 
    //id主键
    private Integer id;
    //品牌名称
    private String brandName;
    //企业名称
    private String companyName;
    //排序字段
    private Integer ordered;
    //描述信息
    private String description;
    //状态 0：禁用 1：启用
    private Integer status;
    public Brand(Integer id, String brandName, String companyName, Integer ordered, String description,
                 Integer status) {
        super();
        this.id = id;
        this.brandName = brandName;
        this.companyName = companyName;
        this.ordered = ordered;
        this.description = description;
        this.status = status;
    }
    public Brand() {
    }
    @Override
    public String toString() {
        return "Brand [id=" + id + ", brandName=" + brandName + ", companyName=" + companyName + ", ordered=" + ordered
                + ", description=" + description + ", status=" + status + "]";
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getBrandName() {
        return brandName;
    }
    public void setBrandName(String brandName) {
        this.brandName = brandName;
    }
    public String getCompanyName() {
        return companyName;
    }
    public void setCompanyName(String companyName) {
        this.companyName = companyName;
    }
    public Integer getOrdered() {
        return ordered;
    }
    public void setOrdered(Integer ordered) {
        this.ordered = ordered;
    }
    public String getDescription() {
        return description;
    }
    public void getDescription(String description) {
        this.description = description;
    }
    public Integer getStatus() {
        return status;
    }
    public void setStatus(Integer status) {
        this.status = status;
    }
}

servlet-el servlet文件


package com.ithema.web;
import com.ithema.pojo.Brand;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
@WebServlet("/demo1")
public class Servlet_el extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.准备数据 现在是list集合，以后是数据库
        List brands= new ArrayList();
        brands.add(new Brand(1,"小米公司","小米科技有限公司",100,"为发烧而生",1));
 
        //2.储存带request域中进行转发
        request.setAttribute("brands",brands);
        request.setAttribute("status",1);
 
        //3.进行请求转发
//        request.getRequestDispatcher("el-demo.jsp").forward(request,response);
        request.getRequestDispatcher("jstl-demo.jsp").forward(request,response);
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request, response);
    }
}

jstl-demo.jsp文件


<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
    <title>Titletitle>
head>
<body>
<%--    c:if:用来完成逻辑判断，替换java if else
        1.一般用法是用el表达式来获取值
        2.再用jstl标签上的c:if来判断值是否合乎规则
--%>
<%--<c:if test="true">
    <h1> true h1>
c:if>
<c:if test="false">
    <h1> false h1>
c:if>--%>
<c:if test="${status ==1}">
    <h2>启用status字符串h2>
c:if>
<c:if test="${status !=1}">
    <h2>禁用status字符串h2>
c:if>
body>
html>

pom文件


"1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0modelVersion>
 
    <groupId>org.examplegroupId>
    <artifactId>jsp-demo01artifactId>
    <version>1.0-SNAPSHOTversion>
 
    <properties>
        <maven.compiler.source>18maven.compiler.source>
        <maven.compiler.target>18maven.compiler.target>
    properties>
 
    <packaging>warpackaging>
 
    <build>
        <plugins>
            
            <plugin>
                <groupId>org.apache.tomcat.mavengroupId>
                <artifactId>tomcat7-maven-pluginartifactId>
                <version>2.2version>
            plugin>
            <plugin>
                <groupId>org.apache.maven.pluginsgroupId>
                <artifactId>maven-compiler-pluginartifactId>
                <configuration>
                    <source>17source>
                    <target>17target>
                configuration>
            plugin>
        plugins>
    build>
 
    <dependencies>
        <dependency>
            <groupId>javax.servletgroupId>
            <artifactId>javax.servlet-apiartifactId>
            <version>3.1.0version>
            <scope>providedscope>
        dependency>
        
        <dependency>
            <groupId>commons-iogroupId>
            <artifactId>commons-ioartifactId>
            <version>2.6version>
        dependency>
        
        <dependency>
            <groupId>org.mybatisgroupId>
            <artifactId>mybatisartifactId>
            <version>3.5.5version>
        dependency>
        
        <dependency>
            <groupId>mysqlgroupId>
            <artifactId>mysql-connector-javaartifactId>
            <version>8.0.29version>
        dependency>
        
        <dependency>
            <groupId>junitgroupId>
            <artifactId>junitartifactId>
            <version>4.13.2version>
            <scope>Testscope>
        dependency>
        
        <dependency>
            <groupId>org.slf4jgroupId>
            <artifactId>slf4j-apiartifactId>
            <version>1.7.36version>
        dependency>
        
        <dependency>
            <groupId>ch.qos.logbackgroupId>
            <artifactId>logback-classicartifactId>
            <version>1.2.3version>
        dependency>
        
        <dependency>
            <groupId>ch.qos.logbackgroupId>
            <artifactId>logback-coreartifactId>
            <version>1.2.3version>
        dependency>
        <dependency>
            <groupId>jstlgroupId>
            <artifactId>jstlartifactId>
            <version>1.2version>
        dependency>
        <dependency>
            <groupId>taglibsgroupId>
            <artifactId>standardartifactId>
            <version>1.1.2version>
        dependency>
    dependencies>
project>

效果

2.c:forEach标签相当于Java中的foreach循环

1.:相当于for循环

*items：被遍历的容器

*var：遍历产生的临时变量

*varStatus：遍历状态对象

*index属性从0开始计数

*count属性从1开始计数

（例如，在数据库中的id可能会有断层，而用数据库中的id当作序号的话，会在显示页面造成断层，从而对阅读者产生不好的影响，所以就会使用varStatus这么一个方法）

示例:


        ${brand.id}
        ${brand.brandName}
        ${brand.companyName}
        ${brand.ordered}
        ${brand.description}
        ${brand.status}


2.${brand.id}代表的不是实体类中的属性变量的名称，而是找到getID这个方法，获取值

实体类brand（和上面的是一样的，所以就不在写了）

servlet-el servlet文件


package com.ithema.web;
 
import com.ithema.pojo.Brand;
 
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
 
@WebServlet("/demo1")
public class Servlet_el extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.准备数据 现在是list集合，以后是数据库
        List brands= new ArrayList();
        brands.add(new Brand(1,"小米公司","小米科技有限公司",100,"为发烧而生",1));
        brands.add(new Brand(2,"华为","华为科技有限公司",10,"不为发烧而生",0));
        brands.add(new Brand(3,"锤子","锤子科技有限公司",99,"为破产而胜",1));
 
        //2.储存带request域中进行转发
        request.setAttribute("brands",brands);
        request.setAttribute("status",1);
 
        //3.进行请求转发
//        request.getRequestDispatcher("el-demo.jsp").forward(request,response);
//        request.getRequestDispatcher("jstl-demo.jsp").forward(request,response);
        request.getRequestDispatcher("jstl-for-demo.jsp").forward(request,response);
 
    }
 
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request, response);
    }
}

jstl-for-demo.jsp文件


<%--
  Created by IntelliJ IDEA.
  User: HP
  Date: 2022/8/20
  Time: 16:21
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
    <title>Titletitle>
head>
<body>
<table border="1" cellspacing="0" width="800">
    <tr>
        <th>序号th>
        <th>品牌名称th>
        <th>企业名称th>
        <th>排序th>
        <th>品牌介绍th>
        <th>状态th>
        <th>操作th>
 
    tr>
<c:forEach items="${brands}" var="brand" varStatus="status">
    <tr align="center">
<%--        <td>${brand.id}td>--%>
        <td>${status.count}td>
        <td>${brand.brandName}td>
        <td>${brand.companyName}td>
        <td>${brand.ordered}td>
        <td>${brand.description}td>
        <c:if test="${brand.status == 0 }">
            <td>禁用td>
        c:if>
        <c:if test="${brand.status == 1 }">
            <td>启用td>
        c:if>
        <td><a href="#">修改a>/<a href="#">删除a>td>
    tr>
c:forEach>
table>
body>
html>

效果

3. c:forEach标签相当于Java中的for循环（简单for循环）

*begin：开始数

*end ：结束数

*step ：步长

示例：

for循环

相当于

for（int i = 0，i<=10，i++）{

system.out.println（”for循环“）；

}

效果

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原文地址：https://blog.csdn.net/qq_51272114/article/details/126440607

jsp JSTL标签详细示例（c:if与c:forEach）

1.c:if标签 相当于Java中的if else标签

2.c:forEach标签 相当于Java中的foreach循环

3. c:forEach标签 相当于Java中的for循环（简单for循环）

for循环

1.c:if标签相当于Java中的if else标签

2.c:forEach标签相当于Java中的foreach循环

3. c:forEach标签相当于Java中的for循环（简单for循环）