1．用戶端上傳檔案
用戶端通過一個Jsp頁面，上傳檔案到伺服器，該Jsp頁面必須含有File類表單，並且表單必須設定enctype="multipart/form- data"。提交表單時通過內建對象request，request.getInputStream();方法獲得一個輸入資料流。
在上傳檔案時，會有附加資訊，如下所示： -----------------------------7d71042a40328
Content-Disposition: form-data; name="fileforload"; filename="C:/Documents and Settings/ZJ/案頭/book.txt"
Content-Type: text/plain
//此處為檔案內容
-----------------------------7d71042a40328
Content-Disposition: form-data; name="submit" commit
-----------------------------7d71042a40328-- 附加資訊大小為297位元組（不確定這個值，測試得到），可通過request.getContentLength()>297來判斷是否上傳了檔案還是提交Null 字元串。
2．測試
fileupload.jsp負責提交檔案，accept.jsp負責實現上傳功能。
fileupload.jsp <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> accept.jsp <html>
<head>
<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> 伺服器端得到的上傳檔案I like.txt，取名為test.txt -----------------------------7d75b1540328
Content-Disposition: form-data; name="fileforload"; filename="C:/Documents and Settings/ZJ/案頭/I like.txt"
Content-Type: text/plain 我喜歡駕馭著代碼在風馳電掣中創造完美;
我喜歡操縱著代碼在隨心所欲中體驗生活;
我喜歡用心情代碼編製我小小的與眾不同;
每一段新的代碼在我手中延生對我來說就象觀看刹那花開的感動;
我不需要焦點.因為我就是焦點! -----------------------------7d75b1540328
Content-Disposition: form-data; name="submit" commit
-----------------------------7d75b1540328--
3．去除附加資訊
按照HTTP協議，檔案表單提交的資訊中，前4行和後5行是表單本身的資訊，中間部分才是上傳的檔案的內容。下例對上傳的檔案進行處理，擷取檔案名稱，並去除附加資訊。
4．測試
fileupload.jsp不變，accept.jsp修改如下： <html>
<head>
<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>
（註：如果檔案名稱是中文，會出現亂碼。）
5．檔案下載
Jsp內建對象response調用方法getOutputStream（）可以擷取一個指向客戶的輸出資料流，伺服器將檔案寫入這個流，然後可下載此檔案。
6．測試
download.jsp顯示下載選項，LoadFile.java（Servlet）負責下載檔案。
download.jsp <html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GB18030">
<title>download page</title>
</head>
<body>
<a href=loadFile>Download:test.zip</a>
</body>
</html> LoadFile.java package com.zj.sample; import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream; import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse; @SuppressWarnings("serial")
public class LoadFile extends HttpServlet{
public void doGet(HttpServletRequest request,HttpServletResponse response)
throws IOException,ServletException{
OutputStream o=response.getOutputStream();
byte b[]=new byte[1024];
//the file to download.
File fileLoad=new File("d:/temp","test.rar");
//the dialogbox of download file.
response.setHeader("Content-disposition",
"attachment;filename="+"test.rar");
//set the MIME type.
response.setContentType("application/x-tar");
//get the file length.
long fileLength=fileLoad.length();
String length=String.valueOf(fileLength);
response.setHeader("Content_Length",length);
//download the file.
FileInputStream in=new FileInputStream(fileLoad);
int n=0;
while((n=in.read(b))!=-1){
o.write(b,0,n);
}
}
public void doPost(HttpServletRequest request,HttpServletResponse response)
throws IOException,ServletException{
doGet(request,response);
} } web.xml（註冊servlet） <servlet>
<servlet-name>LoadFileServlet</servlet-name>
<servlet-class>com.zj.sample.LoadFile</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LoadFileServlet</servlet-name>
<url-pattern>/loadFile</url-pattern>
</servlet-mapping>
