servlet实现文件上传与下载功能

public class FileUploadServlet extends httpservlet {
 public void doPost(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {
 request.setCharacterEncoding("utf-8");
 response.setContentType("text/html;charset=utf-8");
  
 String path = request.getSession().getServletContext().getRealPath("/WEB-INF");
 //解决缓存大小，要不然你的内存会爆的。
 DiskFileItemFactory diskFileItemFactory = new DiskFileItemFactory(1024 * 10,new File(path + "/" + "tmp2") );
 ServletFileUpload fileUpload = new ServletFileUpload(diskFileItemFactory);
 
 List<FileItem> l = null;
 try {
 l = fileUpload.parseRequest(request);
 
 FileItem f2 = l.get(0);
 
 //解决文件存放在WEN_INF目录下问题
 
 path = path + "/tmp";
 
 //解决浏览器传递绝对路径问题
 String name = f2.getName();
 
 int i = name.lastIndexOf("/");
 if(i != -1) {
 name = name.substring(i);
 }
 
 //解决文件重名问题
 name = (UUID.randomUUID().toString().replace("-","").trim()) + name;
 
 
 //文件打散问题解决方法演示之hash打散
 int has = name.hashCode();
 //转换位16进制位，我们使用前两个值来判断
 
 String hex = Integer.toHexString(has);
 path = path + "/" + hex.charAt(0) + "/" + hex.charAt(2) ;
 File file = new File(path);
 if(! file.exists()) {
 file.mkdirs();
 }
 
 f2.write(new File(path + "/" + name));
 request.setAttribute("msg","恭喜你，上传成功了！");
 request.getRequestDispatcher("/index.jsp").forward(request, response);
 
 } catch (Exception e) {
 request.setAttribute("msg",e.getMessage());
 request.getRequestDispatcher("/index.jsp").forward(request, response);
 }
 }
}

public void doGet(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {
 
 String mimeType = request.getSession().getServletContext().getMimeType("\\WEB-INF\\tmp\\2\\5\\"
 + "87bd61a4b7c346a5a2e6c072de84acda5.JdbcUtils处理多线程并发访问问题.avi");
 //解决文件名乱码问题
 String filename = "87bd61a4b7c346a5a2e6c072de84acda5.JdbcUtils处理多线程并发访问问题.avi";
 filename = encoding(filename, request);
 //两个请求头
 response.setHeader("Content-Type",mimeType);
 response.setHeader("Content-Disposition","attachment;filename=" + filename);
 ServletOutputStream out = response.getOutputStream();
 String path = request.getSession().getServletContext().getRealPath("\\WEB-INF\\tmp\\2\\5\\"
 + "87bd61a4b7c346a5a2e6c072de84acda5.JdbcUtils处理多线程并发访问问题.avi");
 File file = new File(path);
 
 FileInputStream inputStream = new FileInputStream(file);
 
 IOUtils.copy(inputStream, out, 1024*1024);
 
 }
 
 private String encoding(String filename,HttpServletRequest req) throws UnsupportedEncodingException {
 String user_agent = req.getHeader("User-Agent");
 String encodingFileName = null;
 if(user_agent.contains("Firefox")) {
 //按道理来说应该使用 BASE64Encoder进行编码，但是不知道为什么不能成功
 
 //那我们只能使用这种方式了
 encodingFileName = new String(filename.getBytes("UTF-8"), "ISO-8859-1");
 }
 else {
 encodingFileName = URLEncoder.encode(filename,"utf-8");
 }
 return encodingFileName;
 }
 
}