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：
-----------------------------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--
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
<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>
<%@ 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>
下载，采用servlet
web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<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>
</web-app>
download.jsp做测试
<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>
写servlet
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;
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);
}
}
经过测试，完全可以实现，希望与大家分享......................