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JavaWeb学习心得之JSP标签

2017-10-28 08:56 369 查看
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;
%>
&
4000
lt;!-- 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：

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