File Download in Servlets

[ford Darcy Jr]

Hi,

I am able to upload files using com.oreilly.servlet.MultipartRequest.
But the problem is the user should be able to view the uploaded file. Can anybody please let me know how to go about achieving this.

Thanks.

[James Carman]

You can stream it back to them if you want using the ServletOutputStream found on the response. However, if this type of file needs some sort of handler on the client (MS Word, JPG, etc.), then you will have to set the contentType and contentLength properties on the response also. For JPG images...

byte[] imageData = <get your image data from disk, db, wherever here>;
response.setContentType( "image/jpg" );
response.setContentLength( imageData.length );
response.getOutpuStream().write( imageData );

[ford Darcy Jr]

Hi James Carman,

Thanks for your response. But can you please provide me with an sample code which will give me an idea as to how to achieve this.

Thanks.

[James Carman]

Where are your files stored (filesystem directory relative to the servlet context root, database, etc.)? What type of files are they (JPG, PDF, Word, MP3 :-)?
[ February 16, 2005: Message edited by: James Carman ]

[Stan James]

I show a little upload confirmation page with a link to the file. Could you just redirect them to the file URL?

[James Carman]

Originally posted by Stan James:
I show a little upload confirmation page with a link to the file. Could you just redirect them to the file URL?

If you're putting the file somewhere where it can be served by the "default" servlet (the one that serves static content), then by all means just use a link. Just make sure you save the file with the appropriate extension and you have the mime type mapping set up properly (probably already done for you).

[ford Darcy Jr]

Hi James Carman,

I am able to upload all file types: text, word and pdf for now. The files are stored on the server.

I hope this helps.

Thanks.

[ford Darcy Jr]

Hi,

Still struggling with File Download in servlets. Can anybody please tell me how to achieve this.

Thanks.

[James Carman]

When you say that the files are stored on the server, are they available to the world via a regular URL, no servlet necessary? If so, then just use regular URLs to access them.

[Carmon Colvin]

I found this thread through google and am trying to do something simular with a servlet.

Here is my situation. I am writing a website for a client that has software to download. They only want it available for people to download if they have "registered" and then received an email with instructions for download. They do not want the software to be accessible via a normal URL link.

Here is what I have so far.

 
 
  protected void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException
  {
    
    String action = request.getParameter("action");
 
    
    // make sure the "action" is legal
    if (action == null)
    {
      // TODO send user to an error page
    } 
    else if (action.equals("download"))
    {
      // check the validation code against database
      boolean allowDownload = validateDownload(request.getParameter("validation"));
 
      // if validation number is valid allow download, otherwise error
      if (allowDownload)
      {
        // load the file and send it to the user
        // get the file
        File file = new File("C:/java/tmp/test.zip");
        FileInputStream fis = new FileInputStream(file);
        // convert the file to bytes
        byte[] fileBytes = new byte[(int)file.length()];
        fis.read(fileBytes);
        // send the file
        response.setContentType("image/zip");
        response.setContentLength( fileBytes.length );
        response.getOutputStream().write( fileBytes );
      }
      else
      {
        // TODO send user to an error page
      }
    }

It works great, except.
1: This will not work if the file size is larger than Integer.MAX_VALUE. that is not a big issue but could be in the future. Is there anyway around this?

2: The "File name" in the Internet Explorer file download prompt takes on the name of the servlet. And "File type" is blank. Is there anyway to specify a file name and extension?


FYI: An example of how a "user" would access this is with a URL that looks like this.
http://localhost:8080/modeaus/DownloadRequest?action=download&validation=83ZIQU3892

[Ben Souther]

Use Buffered streams.
In this one, I'm using ServletContext().getResourceAsStream but you could just as easily use a FileInputStream for getting the file.

  
    try{
            in = new BufferedInputStream(
                getServletContext().
                    getResourceAsStream("WEB-INF" + filename));
            // -----^ A fileInputStream would work here as well.
                                                                                
            response.setContentType(contentType);
            response.setHeader("Content-Disposition",
                               " inline; filename=" + filename);
                                                                                
            ServletOutputStream out = response.getOutputStream();
                                                                                
            byte[] buffer = new byte[4 * 1024];
                                                                                
            int data;
            while((data = in.read(buffer)) != -1){
                out.write(buffer, 0, data);
            }
            out.flush();
        }catch(Exception e){
 

[Carmon Colvin]

Thanks, that is exactly what I needed.

Originally posted by Ben Souther:
[QB]Use Buffered streams.
In this one, I'm using ServletContext().getResourceAsStream but you could just as easily use a FileInputStream for getting the file.

[Sean Sullivan]

Here's an example web application that demonstrates file upload and file download:

http://strutsblobapp.sourceforge.net/

Cheers,

-Sean

[Horatio Westock]

Just to add to this thread, I have code almost the same as that sourceforge example. I've wondered how to make it support resume, but I've never really spent much time on it. I suppose the headers give info on the offset to start at, then you just begin writing out from that offset.

I remember looking into this before and my problem was that, as there was no session, they were always being redirected to login on every request. Then I forgot about it.

Has anyone done this successfully?