下载文件时使用PrintWriter

Question

I have a requirement, where i need to process a set of files and create a compressed zip file out of it and then use it for download. I am using a Servlet for downloading that file, but the download takes quite sometime. So i want the user to know that the servlet is processing the request through a print writer output messsage instead of showing him a blank screen.But everytime i use a printwriter to write something to the screen, the message takes a lot of time to show on the screen and the file doesnt download. How can i achieve this? Any ides? Thanks.

Here's my code

OutputStream oStream = null;
    DataInputStream dInput = null;
    File file = new File(("PATH"));
    int length = 0;
    try{
        DownloadServerLogs.processLogs();
        oStream = res.getOutputStream();
        res.setContentType("application/zip");
        res.setContentLength((int)file.length());
        res.setHeader("Content-Disposition",
                         "attachment;filename=\"" + file.getName() + "\"" );
        byte[] bbuf = new byte[BYTES_DOWNLOAD];
        dInput = new DataInputStream(new FileInputStream(file));

        while ((dInput != null) && ((length = dInput.read(bbuf)) != -1))
        {
            oStream.write(bbuf,0,length);
        }
        dInput.close();
        oStream.flush();
        oStream.close();
    }catch(Exception e){
        Utility.getLogger().error(e.getMessage(), e);
    }

Answer 1

我猜最好通过使用Javascript之类的消息向客户端显示消息（假设您正在使用AJAX来调用servlet）。

Answer 2

Well, it's probably not that safe to do it that way. I'd have a look at the answer below. Not that it's your exact problem, but might be similar.

Most efficient way to create InputStream from OutputStream

Effectively, you are reading and writing on the same thread and my guess is that with the addition of the PrintWriter you are getting deadlocked somewhere.