import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class Download extends HttpServlet
{
public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException
{
try
{
//这里你可以做些其他的事情

response.setContentType("application/octet-stream");
response.setHeader("Content-Disposition", "attachment; filename="你要在保存窗口中显示的保存文件名"");

ServletOutputStream out = response.getOutputStream();
BufferedReader br=new BufferedReader(new FileReader(要下载的的文件名));

String line=br.readLine();
while (line!=null)
{
out.write(line.getBytes());
out.println();
line=br.readLine();
}
out.close();
br.close();
}
catch (Exception e)
{
System.out.println(e);
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException
{
doGet(request, response);
}
}
就是这么简单

版主提示：
这里的代码在做二进制文件下载的时候会有问题，因为这里使用到了BufferedReader，而这个类是为读“字符”而准备，需要按“字节”来读的时候，请使用InputStream来做。