本文通过逐步实验演示了文件上传的基本过程和技术要点。首先介绍了默认设置下仅上传文件路径的情况，并展示了如何通过更改form的enctype属性来正确实现文件上传。
（一）从底层透析文件上传的实现，此时并没有介入struts2
1、upload.jsp，在form中属性method默认为get，涉及文件上传时必须改为post，默认enctype="application/x-www-form-urlencoded" ，我们暂且不修改，看会有什么结果
1
<%@ page language="java" contentType="text/html; charset=GBK"
2
pageEncoding="GBK"%>
3
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
4<html>
5 <head>
6 <meta http-equiv="Content-Type" content="text/html; charset=GB18030">
7 <title>Insert title here</title>
8 </head>
9 <body>
10 <form action="result.jsp" method="post"
11 enctype="application/x-www-form-urlencoded">
12 Information:
13 <input type="text" name="info">
14 <br>
15 File:
16 <input type="file" name="file">
17 <br>
18 <input type="submit" name="submit" value=" submit ">
19 </form>
20 </body>
21</html>
result.jsp<%@ page language="java" contentType="text/html; charset=GBK"2
pageEncoding="GBK"%>3
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">4
<html>5
<head>6
<meta http-equiv="Content-Type" content="text/html; charset=GB18030">7
<title>Insert title here</title>8
</head>9
<body>10
<form action="result.jsp" method="post"11
enctype="application/x-www-form-urlencoded">12
Information:13
<input type="text" name="info">14
<br>15
File:16
<input type="file" name="file">17
<br>18
<input type="submit" name="submit" value=" submit ">19
</form>20
</body>21
</html>
1<%@ page language="java" contentType="text/html; charset=GBK"
2 pageEncoding="GBK"%>
3<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
4<html>
5 <head>
6 <meta http-equiv="Content-Type" content="text/html; charset=GB18030">
7 <title>Insert title here</title>
8 </head>
9 <body>
10 Information:<%=request.getParameter("info")%><br>
11 File:<%=request.getParameter("file")%><br>
12 </body>
13</html>
结果：<%@ page language="java" contentType="text/html; charset=GBK"2
pageEncoding="GBK"%>3
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">4
<html>5
<head>6
<meta http-equiv="Content-Type" content="text/html; charset=GB18030">7
<title>Insert title here</title>8
</head>9
<body>10
Information:<%=request.getParameter("info")%><br>11
File:<%=request.getParameter("file")%><br>12
</body>13
</html>
2、修改result.jsp页面代码，输出读入的流
<%@ page import="java.io.*"%>
<body> <%
InputStream is = request.getInputStream(); BufferedReader br = new BufferedReader(new InputStreamReader(is)); String buffer = null; while ((buffer = br.readLine()) != null) { out.print(buffer + "<br>"); } %> </body>
这个结果可以断定，文件的上传并没有成功，而仅仅是上传了文件的路径信息而已
3、把upload.jsp中form的enctype属性改为enctype="multipart/form-data"
<form action="result.jsp" method="post" enctype="multipart/form-data"> Information: <input type="text" name="info"> <br> File: <input type="file" name="file"> <br> <input type="submit" name="submit" value=" submit "> </form>
说明文件上传是成功的。
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