JSTL(JavaServer Page Standard Tag Library)：JSP标准标签库。它封装了JSP应用的通用核心功能。
1.准备工作
使用JSTL前需要下载所需文件，下载地址及安装教材可参阅：http://www.runoob.com/jsp/jsp-jstl.html
测试类 Person.java
public class Person { ???private String name; ???private String sex; ???private int age; ???????public String getName() { ???????return name; ???} ???????public void setName(String name) { ???????this.name = name; ???} ???public String getSex() { ???????return sex; ???} ???public void setSex(String sex) { ???????this.sex = sex; ???} ???public int getAge() { ???????return age; ???} ???public void setAge(int age) { ???????this.age = age; ???}}2、c:out标签：类似out.printf(xxx)
<%@ 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><html><head><meta charset="UTF-8"><title>Insert title here</title></head><body> ????????<% ???????request.setAttribute("requestAttribute", "requestValue"); ???%> ???????<jsp:useBean id = "per" class = "com.myclass.Person" scope = "request" /> ?<!-- Person per = new Person()--> ???????<jsp:setProperty name = "per" property = "name" value = "zhansan"/> ????????????????<c:out value = "zhansan"/><br> ????????????????????????<!-- out标签直接输出字符串 --> ???<c:out value = "${requestAttribute}"></c:out><br> ?????<!-- out标签输出属性--> ???<c:out value = "${per.name}"></c:out><br> ?????????????<!-- out标签输出对象中属性 --> ???????<!-- 当输出为空时，输出默认值--> ???<c:out value = "${requestAttri}" default = "该属性不存在！"/><br> ????<!-- default设置默认值 --> ???<c:out value = "${requestAttri}">该属性不存在</c:out><br> ????????????<!-- 标签体设置默认值 --> ???<c:out value = "<%=null %>" default = "该属性不存在！"/> ????????</body></html>3、c:set标签：主要用于设置属性、对象中属性的值。类似setXXX，setAttribute(var,value);
<head><meta charset="UTF-8"><title>Insert title here</title></head><body> ????????<% ???????request.setAttribute("requestAttri", "requestValue"); ???%> ????????<jsp:useBean id = "per" class = "com.myclass.Person" scope = "request" /> ?<!-- Person per = new Person()--> ???????<c:set var = "test" value = "test"/> ??<!-- 没有指定属性范围，默认是pageScope --> ???${pageScope.test} ???????<!-- <c:set var = "属性名称" value = "属性值" ?scope = "属性作用域" /> --> ???<c:set var = "sessionName" value = "sessionValue" scope = "session"/> ?<!-- 在指定范围中设置属性 （value属性设置值） --> ???<!-- 相当于session.setAttribute("sessionName","sessionValue") ?--> ???<c:out value = "${sessionName}" /> ???
<!-- <c:set var = "属性名称" scope = "属性作用域"> 属性值 </c:set> --> ???<c:set var = "requestName" scope = "request">requestValue</c:set> ? <!--在指定范围中设置属性 （标签体设置值）--> ???<!-- 相当于request.setAttribute("requestName","requestValue") ?--> ???<c:out value = "${requestName}" /> ???
<!-- <c:set target = "对象名称" property = "属性名" value = "属性值"> ?--> ???<c:set target = "${per}" property = "name" value = "zhangsan"/> ?? <!--通过标签 设置对象属性 类似 ?per.name = "zhangsan"--> ???<c:out value="${per.name}"></c:out> ???<c:out value="${per}"></c:out> ?<!-- 此处的${per} 类似 System.out.print(per)--> ???</body></html>4、c:remove标签:移除属性，类似（xxx.remove(name)）
<%@ page language="java" contentType="text/html; charset=UTF-8" ???pageEncoding="UTF-8"%><%@ page import = "java.util.*,com.myclass.*" %><%@ taglib uri = "http://java.sun.com/jsp/jstl/core" prefix = "c" %><!DOCTYPE html><html><head><meta charset="UTF-8"><title>Insert title here</title></head><body> ????<c:set var = "testRemove" value = "value" scope = "session"/> ???<!-- <c:remove var = "属性名" scoep = "[page|request|session|application]" /> 删除指定作用域中的var属性--> ???<c:remove var="testRemove" scope="session"/> ?<!-- 类似 session.removeAttribute("testRemove") --> ???<c:out value = "${tempRemove }" default="该属性不存在"/> ???????</body></html>5、c:if 标签:用于判断，类似if(test == [true | false]){语句}
<%@ taglib uri = "http://java.sun.com/jsp/jstl/core" prefix = "c" %><!DOCTYPE html><html><head><meta charset="UTF-8"><title>Insert title here</title></head><body> ???????<c:set var = "age" value = "19" scope = "session"/> ???????<%-- ??<c:if test = "判断条件" var = "属性名" scope = "设置保存范围" ?/> ??--%> ???????<!-- 判断的结果（true|false）会存储在var中 --> ???????<c:if test = "${age >= 18 }" var="isAdult" scope = "session" > ???????????<h2> 成年</h2> ?<!-- 满足条件执行的语句 --> ???????</c:if> ???????<c:if test = "${!isAdult}" > ?<!-- !isAdult 和isAdult互反所以只会执行一个 --> ???????????未成年 ???????</c:if> ???????是否成年：${isAdult} ???????</body></html>6、c:choose标签:分支选择，类似switch。
<%@ page language="java" contentType="text/html; charset=UTF-8" ???pageEncoding="UTF-8"%><%@ page import = "java.util.*,com.myclass.*" %><%@ taglib uri = "http://java.sun.com/jsp/jstl/core" prefix = "c" %><!DOCTYPE html><html><head><meta charset="UTF-8"><title>Insert title here</title></head><body> ???????<c:set var = "score" value = "60" scope = "session"/> ???????<c:choose > ???????????<c:when test="${score >= 90}"> 优秀</c:when> ????<!-- test为true则执行对应语句并跳出choose --> ???????????<c:when test="${score >= 80}"> 良好</c:when> ???????????<c:when test="${score >= 70}"> 一般</c:when> ???????????<c:when test="${score >= 60}"> 及格</c:when> ???????????<c:otherwise>不及格</c:otherwise> ??????????????????<!-- 所有选项都不满足则执行otherwise中的语句 --> ???????</c:choose> ???????</body></html>7、c: forEach标签:主要用于输出可迭代对象和控制迭代次数（for）
实现了Collection接口的对象，都可以使用forEach输出。
<%@ taglib uri = "http://java.sun.com/jsp/jstl/core" prefix = "c" %><!DOCTYPE html><html><head><meta charset="UTF-8"><title>Insert title here</title></head><body> ????<!-- forEach输出list --> ???<% ???????List<String> list = new LinkedList<String>(); ???????for(int i = 0; i < 5; i++){ ???????????list.add("赵" + i); ???????} ???????request.setAttribute("list", list); ???%> ???????<c:forEach items = "${list}" var = "li"> ???????<c:out value = "${li}"/><!-- li就代表链表中一个对象（String） --> ???</c:forEach><br> ???????<!-- forEach输出map --> ???<% ???????Map<String,Person> map = new HashMap<String,Person>(); ???????for(int i = 0; i < 5; i++){ ???????????map.put("" + i,new Person("钱" + i, i % 2 == 0 ? "man" : "woman", i)); ???????} ???????request.setAttribute("map",map); ???%> ???<c:forEach items = "${map}" var = "m" ><!-- m代表map中一个对象，可通过m.key获取键，m.value获取值（person对象） --> ???????${m.key } ${m.value.name} ${m.value.sex} ${m.value.age}<br> ????</c:forEach><br> ???????<!-- 控制迭代次数 并输出状态--> ???<table> ???????<td>值</td><td> 是否是第一个</td><td>是否是最后一个</td><td>计数（当前是第几个）</td> ???????<c:forEach var = "i" begin="1" end = "11" step = "2" varStatus="st"> <!-- 步长（step）为2 for(i = 1; i <= 11 ; i += 2 ) --> ???????????????<tr><!-- 迭代的属性 ??????????当前属性是否是第一个 ??????当前属性是否是最后一个 ????计数是第几个属性，从1开始--> ???????????????????????<td>${i }</td><td> ${st.first}</td><td>${st.last }</td><td>${st.count}</td> ???????????????</tr> ???????</c:forEach> ???</table> ???????</body></html>8、forTokens标签: 将字符串分割成子串然后迭代。类“www.google.com”.split(".")
<%@ page language="java" contentType="text/html; charset=UTF-8" ???pageEncoding="UTF-8"%><%@ page import = "java.util.*,com.myclass.*" %><%@ taglib uri = "http://java.sun.com/jsp/jstl/core" prefix = "c" %><!DOCTYPE html><html><head><meta charset="UTF-8"><title>Insert title here</title></head><body> ????????????????<!-- ?0 ???1 ????2 ?--> <!--类似 l[3] = {"www","google","com"}; for(i = 0; i <=2 ; i+=2) printf(l[i]) --> ???????<c:forTokens items="www.google.com" delims="." var = "l" ?begin = "0" end = "2" step = "2"> ???????????${l}<br> ???????</c:forTokens> ???????<!-- items为被切割的字符串，delims 为切割的依据 ??--></body></html>9.c:redirect：重定向将重定向到指定URL。
<%@ page language="java" import = "java.util.*,com.myclass.*" contentType="text/html; charset=UTF-8" ???pageEncoding="UTF-8"%> ??<%@ taglib uri = "http://java.sun.com/jsp/jstl/core" prefix = "c" %><!DOCTYPE html><html><head><meta charset="UTF-8"><title>Insert title here</title></head><body> ???<c:redirect url="http://www.baidu.com"></c:redirect> <!-- 重定向到百度 --> ???????????????????????????????????????</body></html>
自定义标签及自定义实现out、if、forEach标签。
参考资料：
https://blog.csdn.net/qq_42246139/article/details/80623607
http://www.runoob.com/jsp/jsp-jstl.html
1.5 JSP标准标签库（JSTL）(核心标签 out、set、remove、if、choose、forEach、forTokens、redirect)
原文地址：https://www.cnblogs.com/huang-changfan/p/10345924.html