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JSTL技术
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1．JSTL概述
JSTL（JSP Standard Tag Library)，JSP標準標簽庫，可以嵌入在jsp頁面中使用標簽的形式完成業務邏輯等功能。jstl出現的目的同el一樣也是要代替jsp頁面中的腳本代碼。JSTL標準標準標簽庫有5個子庫，但隨著發展，目前常使用的是他的核心庫
標簽庫標簽庫的URI前綴
| Core | http://java.sun.com/jsp/jstl/core | c |
| I18N | http://java.sun.com/jsp/jstl/fmt | fmt |
| SQL | http://java.sun.com/jsp/jstl/sql | sql |
| XML | http://java.sun.com/jsp/jstl/xml | x |
| Functions | http://java.sun.com/jsp/jstl/functions | fn |
2．JSTL導入
需要導兩個包：
jstl.jar
standar.jar
使用jsp的taglib指令導入核心標簽庫
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
3．JSTL核心庫的常用標簽
1）<c:if test=””>標簽
其中test是返回boolean的條件
2）<c:forEach>標簽
使用方式有兩種組合形式：
示例：
1）遍歷List的值
2）遍歷List的值
3）遍歷Map<String,String>的值
4）遍歷Map<String,User>的值
5）遍歷Map<User,Map<String,User>>的值
entry.key-----User
entry.value------List<String,User>
//forEach.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"pageEncoding="UTF-8"%>
<%@ page import="java.util.*" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ page import="beyond.domain.*" %>
<!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><%//模擬List
<String> strListList
<String> strList = new ArrayList
<String>();strList.add("beyond0");strList.add("beyond1");strList.add("beyond2");strList.add("beyond3");request.setAttribute("wsq", strList);//遍歷List
<User>的值List
<User> userList = new ArrayList
<User>();User user1 = new User();//list集合中的第一個元素user1.setId(2);user1.setName("qibao");user1.setPassword("wsq");userList.add(user1);//list集合中的第二個元素User user2 = new User();user2.setId(3);user2.setName("yanyu");user2.setPassword("wsq");userList.add(user2);application.setAttribute("qb", userList);//遍歷Map
<String,String>的值Map
<String,String> strMap = new HashMap
<String,String>();strMap.put("name", "hjj");strMap.put("age", "32");strMap.put("addr", "香港");strMap.put("email", "hjj@qq.com");session.setAttribute("strMap", strMap);//遍歷Map
<String,User>的值Map
<String,User> userMap = new HashMap
<String,User>();userMap.put("user1", user1);userMap.put("user2", user2);session.setAttribute("userMap", userMap); /* //遍歷Map<User,Map
<String,User>>的值Map<User,Map
<String,User>> mapMap = new HashMap<User,Map
<String,User>>();mapMap.put(user1,userMap);mapMap.put(user2,userMap);session.setAttribute("mapMap", mapMap); */%>
<h1>取出strList的數據
</h1><c:forEach items="${wsq}" var="str">${str}
<br/></c:forEach><h1>取出userList的數據
</h1><c:forEach items="${qb}" var="user" >user的name:${user.name}------------user的password:${user.password}
<br/></c:forEach><h1>取出strMap的數據
</h1><c:forEach items="${strMap}" var="entry">${entry.key}---------------${entry.value}
<br/></c:forEach><h1>取出userMap的數據
</h1><c:forEach items="${userMap}" var="entry" >${entry.key}--------------${entry.value.id}--------------${entry.value.name}--------------${entry.value.password}
<br/></c:forEach><%--
<h1>取出mapMap的數據
</h1><c:forEach items="${mapMap}" var="enter">${entry.key.key}--------------${entry.value.value.id}--------------${entry.value.name}--------------${entry.value.password}
<br/></c:forEach> --%>
</body>
</html>
//userLogin.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"pageEncoding="UTF-8"%>
<%@ page import= "beyond.domain.*" %>
<!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><% User user = new User();user.setId(1014);user.setName("wsq");user.setPassword("wsq");session.setAttribute("user", user);/* 把user放到session域當中 */%>
</body>
</html>
//jstl.jsp
<%@ 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 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><%request.setAttribute("count", 1014);%>
<c:if test="${count==1014}">nice you are right！！
</c:if><c:if test="1==1">beyond
</c:if><c:if test="1!=1">sq
</c:if><c:forEach begin="0" end="5" var="i">${i}
<br/></c:forEach><c:forEach items="${productList}" var="pro">${pro.pname}
</c:forEach></body>
</html>
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