JavaWeb学习心得之JSP标签

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最新推荐文章于 2022-05-03 15:36:27 发布

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分类专栏： JavaWeb学习笔记文章标签：标签 include forward param

本文链接：https://blog.youkuaiyun.com/qq_36652337/article/details/78372747

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本文探讨了JavaWeb中的JSP标签，包括其作为提供业务逻辑功能的Jsp Action元素的角色，避免在页面上直接使用Java代码。文章详细介绍了三个常用标签：<jsp:include>、<jsp:forward>和<jsp:param>的用法，展示了如何通过它们实现页面的动态包含、请求转发以及传递参数。

一、JSP标签概念

JSP标签也称之为Jsp Action元素，它用于在JSP页面中提供业务逻辑功能，避免直接写Java代码。

二、常用JSP标签

常用标签：

<jsp：include>
<jsp：forward>
<jsp：param>

1.<jsp：include>标签

作用：用于把另外一个资源的内容插入当前JSP页面的内容中，这种JSP在执行时的引入方式称为动态引入。

语法：<jsp:include page="url" flush="true" />,其中page属性指定被引入资源的路径，flush是否刷新当前JSP页面已输出的内容。

引入资源：

<jsp:include>标签和include指令的区别

head.jsp文件

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


<!-- Mirrored from www.zi-han.net/theme/hplus/login_v2.html by HTTrack Website Copier/3.x [XR&CO'2014], Wed, 20 Jan 2016 14:19:49 GMT -->
<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0">

    <title>test</title>
</head>

<body>
	<%
		int i=1000;
	%>
	<!-- 用jsp标签引入资源内容 -->
	<p>head页面中i的值为<%=i %></p>
</body>
</html>

include指令是静态引入

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


<!-- Mirrored from www.zi-han.net/theme/hplus/login_v2.html by HTTrack Website Copier/3.x [XR&CO'2014], Wed, 20 Jan 2016 14:19:49 GMT -->
<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0">

    <title>test</title>
</head>

<body>
	<%
		int i=100;
	%>
	<!-- 用jsp标签引入资源内容 -->
	<p>test页面中i的值为<%=i %></p>
	<%@include file="/head.jsp" %>
</body>
</html>

访问结果：便宜错误

以上结果，是因为include指令是先引入在处理，当head.jsp引入后，head.jsp和test.jsp中同时存在相同的变量i，所以有冲突，导致编译异常。

<jsp:include>动态引入

	<%@ page language="java" contentType="text/html; charset=UTF-8"
		pageEncoding="UTF-8"%>
	<!DOCTYPE html>
	<html lang="en">
	
	
	<!-- Mirrored from www.zi-han.net/theme/hplus/login_v2.html by HTTrack Website Copier/3.x [XR&CO'2014], Wed, 20 Jan 2016 14:19:49 GMT -->
	<head>
	    <meta charset="utf-8">
	    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0">
	
	    <title>test</title>
	</head>
	
	<body>
		<%
			int i=100;
		%>
		<!-- 用jsp标签引入资源内容 -->
		<p>test页面中i的值为<%=i %></p>
		<jsp:include page="/head.jsp"></jsp:include>
	</body>
	</html>

访问结果

<jsp:include>动态引入，是先处理两个JSP页面，然后再引入内容。

2.<jsp:forward>标签

作用：用于把请求转发给另外一个资源。

语法：<jsp:forward page="url"/> page属性用于指定请求转发资源路径

示例

test.jsp

	<%@ page language="java" contentType="text/html; charset=UTF-8"
		pageEncoding="UTF-8"%>
	<!DOCTYPE html>
	<html lang="en">
	
	
	<!-- Mirrored from www.zi-han.net/theme/hplus/login_v2.html by HTTrack Website Copier/3.x [XR&CO'2014], Wed, 20 Jan 2016 14:19:49 GMT -->
	<head>
	    <meta charset="utf-8">
	    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0">
	
	    <title>test</title>
	</head>
	
	<body>
		<!-- 用jsp标签转发 -->
		<jsp:forward page="/test1.jsp"></jsp:forward>
	</body>
	</html>

test1.jsp

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


<!-- Mirrored from www.zi-han.net/theme/hplus/login_v2.html by HTTrack Website Copier/3.x [XR&CO'2014], Wed, 20 Jan 2016 14:19:49 GMT -->
<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0">

    <title>test</title>
</head>

<body>
	<p>转发后的页面</p>
</body>
</html>

访问结果：

3.<jsp:param>标签

作用：当使用<jsp:include>和<jsp:forward>标签引入或将请求转发给其它资源时，可以使用<jsp:param>标签向这个资源传递参数。

语法：

<jsp:include page="url"><jsp:param name="" value="" /></jsp:include>
<jsp:forward page="url"><jsp:param name="" value="" /></jsp:forward>

其中，name属性指定参数名，value属性指定参数值

示例1：

test.jsp

	<%@ page language="java" contentType="text/html; charset=UTF-8"
		pageEncoding="UTF-8"%>
	<!DOCTYPE html>
	<html lang="en">
	
	
	<!-- Mirrored from www.zi-han.net/theme/hplus/login_v2.html by HTTrack Website Copier/3.x [XR&CO'2014], Wed, 20 Jan 2016 14:19:49 GMT -->
	<head>
	    <meta charset="utf-8">
	    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0">
	
	    <title>test</title>
	</head>
	
	<body>
		<!-- 用jsp标签转发 -->
		<jsp:forward page="/test1.jsp">
			<jsp:param value="hello" name="param1"/>
			<jsp:param value="world" name="param2"/>
		</jsp:forward>
	</body>
	</html>

test1.jsp

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


<!-- Mirrored from www.zi-han.net/theme/hplus/login_v2.html by HTTrack Website Copier/3.x [XR&CO'2014], Wed, 20 Jan 2016 14:19:49 GMT -->
<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0">

    <title>test</title>
</head>

<body>
	<p>接收到的参数</p>
	<p><%=request.getParameter("param1") %></p>
	<p><%=request.getParameter("param2") %></p>
</body>
</html>

示例2

test.jsp

	<%@ page language="java" contentType="text/html; charset=UTF-8"
		pageEncoding="UTF-8"%>
	<!DOCTYPE html>
	<html lang="en">
	
	
	<!-- Mirrored from www.zi-han.net/theme/hplus/login_v2.html by HTTrack Website Copier/3.x [XR&CO'2014], Wed, 20 Jan 2016 14:19:49 GMT -->
	<head>
	    <meta charset="utf-8">
	    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0">
	
	    <title>test</title>
	</head>
	
	<body>
		<jsp:include page="/head.jsp">
			<jsp:param value="hello" name="param1"/>
			<jsp:param value="world" name="param2"/>
		</jsp:include>
	</body>
	</html>

test1.jsp

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


<!-- Mirrored from www.zi-han.net/theme/hplus/login_v2.html by HTTrack Website Copier/3.x [XR&CO'2014], Wed, 20 Jan 2016 14:19:49 GMT -->
<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0">

    <title>test</title>
</head>

<body>
	<p>接收到的参数</p>
	<p><%=request.getParameter("param1") %></p>
	<p><%=request.getParameter("param2") %></p>
</body>
</html>

访问结果：