还是求救下载sevlet问题。自行写了一个servlet用于下载文件，但下载完成后，无法实现向用户提示“下载成功”等信息。

Question

NO  我不知道说什么啊。。什么都没有我们怎么说啊 。。

Answer 1

public void  download(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
     HttpSession session = request.getSession();
     UserInfo userInfo = (UserInfo)session.getAttribute("UserInfo");
     if(userInfo==null ){
         userInfo = new UserInfo();
     }
     if(userInfo.getUserCode().equals("")){
         userInfo.setErrorNum("4");
         session.setAttribute("UserInfo",userInfo);
         //response.sendRedirect("error");
         return;
     }
     String downFileName = request.getParameter("FILENAME");
     if(downFileName==null || downFileName.equals("")){
         userInfo.setErrorNum("5");
         session.setAttribute("UserInfo",userInfo);
         //response.sendRedirect("error");
         return;
     }
    response.setContentType( "application/octet-stream" ); // MIME type for pdf doc
    response.setHeader("Content-disposition", "attachment; filename=" +downFileName);
    File file = null;
    try{
       Properties prop = (Properties)getServletContext().getAttribute("property");
       String pathtemp = prop.getProperty("downloadpath");
       file = new File(pathtemp,downFileName);
       if(!file.exists()){
          userInfo.setErrorNum("6");
          session.setAttribute("UserInfo",userInfo);
          //response.sendRedirect("error");
          return;
       }
     }catch(Exception exc){exc.printStackTrace();}
     BufferedInputStream iin = new BufferedInputStream(new java.io.FileInputStream(file));;
     BufferedOutputStream dout = new BufferedOutputStream(response.getOutputStream());;
     try {
           byte[] buffer;
           int length = (new Long(file.length())).intValue();
           buffer = new byte[length];
           try{
           //传送数据
              int once = 0;
              int total = 0;
              while ((total<length) && (once>=0)) {
                 once = iin.read(buffer,total,length);
                 total += once;
                 dout.write(buffer,0,length);
              }
              dout.flush();
              userInfo.setErrorNum("8");
              session.setAttribute("UserInfo",userInfo);
              //response.sendRedirect("error");
          }catch(Exception ex){
              userInfo.setErrorNum("7");
              session.setAttribute("UserInfo",userInfo);
              response.sendRedirect("error");
          }finally{
              try{
                 if(iin!=null){   iin.close();}
                 if(dout!=null){  dout.close();}
              }catch(Exception exc){exc.printStackTrace();}
          }
      }catch(Exception ex) {
              userInfo.setErrorNum("7");
              session.setAttribute("UserInfo",userInfo);
              //response.sendRedirect("error");
      }
      //当下载完成后，想通过out.println()方法输出一段信息提示用户下载是否成功的字样，但服务器控制台上总是提示java.lang.IllegalStateException: response already committed异常，不知如何实现？
  }