跟随小破站学习java web第十一天

最新推荐文章于 2025-08-17 14:41:41 发布

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#jsp #jstl

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本文深入探讨了EL表达式在JavaWeb中的应用，包括直接调用属性和使用empty运算符等内容，并全面解析了JSTL标签库的功能，如set、remove、if、choose和forEach等标签的使用方法。

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!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>

	<% 
		application.setAttribute("name", "zs");
		session.setAttribute("name2", "zs2");
		request.setAttribute("name3", "zs3");
		pageContext.setAttribute("name4", "zs4");
	%>
	
	application:<%=application.getAttribute("name")%><br>
	session:<%=session.getAttribute("name2")%><br>
	request:<%=request.getAttribute("name3")%><br>
	pageContext:<%=pageContext.getAttribute("name4")%><br>

<%-- 	<jsp:forward page="jsp_objectDemo2.jsp"></jsp:forward> --%>
	<a href="jsp_objectDemo2.jsp">demo2</a>

</body>
</html>

注意:当服务器重启时,session却依然有效!

<%@page import="com.atguigu.bean.Student"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!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>
	<%
		int i = 10;
		pageContext.setAttribute("i", i);
		request.setAttribute("i", i);
		session.setAttribute("i", i);
		application.setAttribute("i", i);
	%>
	jsp:<%=i %>
	el:${i} 
	<h1>el取对象及对象的属性值</h1>
	<%
		Student stu = new Student("zhangsan",18);
		request.setAttribute("stu", stu);
	%>
	el:${stu.name }<br>
	jsp:<%=((Student)request.getAttribute("stu")).getName() %>
</body>
</html>

最直观的区别:el可以直接调用属性,但jsp需要强制转换类型!

全局变量:如果没有get方法,变量只能算一个空壳

属性:在类中书写get方法后的变量才算属性

<%@page import="java.util.ArrayList"%>
<%@page import="java.util.List"%>
<%@page import="com.atguigu.bean.Student"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!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>
	<h1>empty运算符</h1>
	<%
		String s = "";
		String s2 = null;
		List<String> list = new ArrayList<String>();
		
		request.setAttribute("s", s);
		request.setAttribute("s2", s2);
		request.setAttribute("list", list);
	%>
	${not empty s}<br>
	${!empty s2}<br>
	${empty list}<br>
</body>
</html>

<%@ 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>
	<%
		int i = 10;
		request.setAttribute("i", i);
	%>
	jsp:<%=i %>
	<h1>JSTL通用标签</h1>
	<c:set var="i" value="100" scope="page"></c:set>
	jstl:<c:out value="${pageScope.i}"></c:out>
	<c:remove var="i" scope="request"/><br>
	el:${i}
</body>
</html>

当<c:set>标签内不设置scope=”…” 默认为最小域page

当<c:remove>标签内不设置scope=”…” 默认全部消除

JSTL选择结构

<%@page import="com.atguigu.bean.User"%>
<%@ 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>
	<h1>JSTL选择结构</h1>
	<c:set target="${requestScope.user }" property="username" value="lisi"></c:set>
	<c:if test="${not empty requestScope.user }">
		user is null
	</c:if>
	end<br>
<!-- 	age<18:未成年	30>age>=18:青年	60>age>=30:中年	80>age>=60:中老年
		age>=80:老年  -->
	<c:set var="age" value="17" scope="session"></c:set>
	<c:choose>
		<c:when test="${sessionScope.age<18 }">
			未成年
		</c:when>
		<c:when test="${sessionScope.age>=18 and sessionScope<30 }">
			青年
		</c:when>
		<c:when test="${sessionScope.age>=30 and sessionScope<60 }">
			中年
		</c:when>
		<c:when test="${sessionScope.age>=60 and sessionScope<80 }">
			中老年
		</c:when>
		<c:otherwise>
			老年
		</c:otherwise>
	</c:choose>
</body>
</html>

JSTL循环结构

<%@page import="java.util.ArrayList"%>
<%@page import="java.util.List"%>
<%@page import="com.atguigu.bean.User"%>
<%@ 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>
	<%
		//list
		List<User> list = new ArrayList<User>();
		list.add(0,new User("zs","123456"));
		list.add(1,new User("lisi","123456"));
		list.add(2,new User("wangwu","123456"));
		session.setAttribute("list", list);
	%>
	
	<h1>循环结构</h1>
	<c:forEach var="i" begin="1" end="100" step="2">
		${i }
	</c:forEach>
	<br>
	<c:forEach items="${sessionScope.list }" var="user">
		username:${user.username }-----password:${user.password}<br>
	</c:forEach>
</body>
</html>