文件上传专栏
1 ．客户端上传文件
客户端通过一个 Jsp 页面，上传文件到服务器，该 Jsp 页面必须含有 File 类表单，并且表单必须设置 enctype="multipart/form-data" 。提交表单时通过内置对象 request ， request.getInputStream(); 方法获得一个输入流。
在上传文件时，会有附加信息，如下所示：
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-----------------------------7d71042a40328
Content-Disposition: form-data; name="fileforload"; filename="C:/Documents and Settings/ZJ/ 桌面 /book.txt"
Content-Type: text/plain
// 此处为文件内容
-----------------------------7d71042a40328
Content-Disposition: form-data; name="submit"
commit
-----------------------------7d71042a40328--
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附加信息大小为 297 字节（不确定这个值，测试得到），可通过 request.getContentLength()>297 来判断是否上传了文件还是提交空字符串。
2 ．测试
fileupload.jsp 负责提交文件， accept.jsp 负责实现上传功能。
fileupload.jsp
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< html >
< head >
< meta http-equiv = "Content-Type" content = "text/html; charset=GB18030" >
< title > This page for FileUpload </ title >
</ head >
< body >
< p > Choose the file for uploading:
< form action = "accept.jsp" method = post enctype = "multipart/form-data" >
< input type = file name = fileforload size = 30 >
< br >
< input type = submit value = commit name = submit >
</ form >
</ body >
</ html >
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accept.jsp
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< html >
< head >
<%@ page language = "java" import = "java.io.*" %>
< meta http-equiv = "Content-Type" content = "text/html; charset=GB18030" >
< title > This page for response </ title >
</ head >
< body >
<%
try {
if (request.getContentLength() > 297) {
InputStream in = request.getInputStream();
File f = new File( "d:/temp" , "test.txt" );
FileOutputStream o = new FileOutputStream(f);
byte b[] = new byte [1024];
int n;
while ((n = in.read(b)) != -1) {
o.write(b, 0, n);
}
o.close();
in.close();
out.print( "File upload success!" );
} else {
out.print( "No file!" );
}
} catch (IOException e) {
out.print( "upload error." );
e.printStackTrace();
}
%>
</ body >
</ html >
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服务器端得到的上传文件 I like.txt ，取名为 test.txt
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-----------------------------7d75b1540328
Content-Disposition: form-data; name="fileforload"; filename="C:/Documents and Settings/ZJ/ 桌面 /I like.txt"
Content-Type: text/plain
我喜欢驾驭着代码在风驰电掣中创造完美 ;
我喜欢操纵着代码在随心所欲中体验生活 ;
我喜欢用心情代码编制我小小的与众不同 ;
每一段新的代码在我手中延生对我来说就象观看刹那花开的感动 ;
我不需要焦点 . 因为我就是焦点 !
-----------------------------7d75b1540328
Content-Disposition: form-data; name="submit"
commit
-----------------------------7d75b1540328--
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3 ．去除附加信息
按照 HTTP 协议，文件表单提交的信息中，前 4 行和后 5 行是表单本身的信息，中间部分才是上传的文件的内容。下例对上传的文件进行处理，获取文件名，并去除附加信息。
4 ．测试
fileupload.jsp 不变， accept.jsp 修改如下：
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< html >
< head >
<%@ page language = "java" import = "java.io.*" %>
< meta http-equiv = "Content-Type" content = "text/html; charset=GB18030" >
< title > The real file </ title >
</ head >
< body >
<% try {
//use sessionid to create a temp file.
String tempFileName=(String)session.getId();
//create the temp file.
File temp= new File( "d:/temp" ,tempFileName);
FileOutputStream o= new FileOutputStream(temp);
if (request.getContentLength()>297){
//write the upload content to the temp file.
InputStream in=request.getInputStream();
byte b[]= new byte [1024];
int n;
while ((n=in.read(b))!=-1){
o.write(b,0,n);
}
o.close();
in.close();
//read the temp file.
RandomAccessFile random= new RandomAccessFile(temp, "r" );
//read Line2 to find the name of the upload file.
int second=1;
String secondLine= null ;
while (second<=2){
secondLine=random.readLine();
second++;
}
//get the last location of the dir char.'//'.
int position=secondLine.lastIndexOf( '//' );
//get the name of the upload file.
String fileName=secondLine.substring(position+1,secondLine.length()-1);
//relocate to the head of file.
random.seek(0);
//get the location of the char.'Enter' in Line4.
long forthEndPosition=0;
int forth=1;
while ((n=random.readByte())!=-1&&(forth<=4)){
if (n== '/n' ){
forthEndPosition=random.getFilePointer();
forth++;
}
}
File realFile= new File( "d:/temp" ,fileName);
RandomAccessFile random2= new RandomAccessFile(realFile, "rw" );
//locate the end position of the content.Count backwards 6 lines.
random.seek(random.length());
long endPosition=random.getFilePointer();
long mark=endPosition;
int j=1;
while ((mark>=0)&&(j<=6)){
mark--;
random.seek(mark);
n=random.readByte();
if (n== '/n' ){
endPosition=random.getFilePointer();
j++;
}
}
//locate to the begin of content.Count for 4 lines's end position.
random.seek(forthEndPosition);
long startPoint=random.getFilePointer();
//read the real content and write it to the realFile.
while (startPoint<endPosition-1){
n=random.readByte();
random2.write(n);
startPoint=random.getFilePointer();
}
random2.close();
random.close();
//delete the temp file.
temp.delete();
out.print( "File upload success!" );
}
else {
out.print( "No file!" );
}
}
catch (IOException e){
out.print( "upload error." );
e.printStackTrace();
}
%>
</ body >
</ html >
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（注：如果文件名是中文，会出现乱码。）
转载自：http://zhangjunhd.blog.51cto.com/113473/19631