java - ServletFileUpload#parseRequest(request) returns an empty list

Question

I have a client application in Android which uses HttpURLConnection to send files to the server. The server uses the Apache Commons FileUpload API to parse the form-data values.

The HttpURLConnection sends this request:

-----------------------------4912995119421
Content-Disposition: form-data; name="deviceid"

9428103
-----------------------------4912995119421
Content-Disposition: form-data; name="countryid"

598
-----------------------------4912995119421
Content-Disposition: form-data; name="number"

98621360
-----------------------------4912995119421
Content-Disposition: form-data; name="file"; filename="2012-12-08 17.42.18.jpg"
Content-Type: image/jpeg

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      @      °      a    
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’    .   ?    0100?       ?    @  ?    °  ?    >  ￡       ¤        ¤        ¤    6  ¤                     
   2012:12:08 17:42:18 2012:12:08 17:42:18    
     d               R98      0100                         (           ¤      T.      ???à JFIF      ?? C @@?? 
-----------------------------4912995119421--

The server code:

    String contentType = request.getContentType();
    if ((contentType.indexOf("multipart/form-data") == -1)) {
        response.setStatus(HttpServletResponse.SC_NOT_FOUND);
        return;
    }


    long maxFileSize = (2 * 1024 * 1024);

    int maxMemSize = (2 * 1024 * 1024);

    DiskFileItemFactory factory = new DiskFileItemFactory();
    // maximum size that will be stored in memory
    factory.setSizeThreshold(maxMemSize);

    // Create a new file upload handler
    ServletFileUpload upload = new ServletFileUpload(factory);
    // maximum file size to be uploaded.

    upload.setSizeMax(maxFileSize);

    List fileItems = upload.parseRequest(request);
    Iterator i = fileItems.iterator();


    //leo primero todas las variables.

    int deviceID = 0;
    int countryID = 0;
    String phoneNumber = "";



    while (i.hasNext()) {
        FileItem fi = (FileItem) i.next();

        if (fi.isFormField()) {
            String variable = fi.getFieldName();
            if (variable.equals("deviceid")) {
                deviceID = Integer.parseInt(fi.getString());
            } else if (variable.equals("countryid")) {
                countryID = Integer.parseInt(fi.getString());
            } else if (variable.equals("number")) {
                phoneNumber = String.valueOf(Long.parseLong(fi.getString()));
            }

        }

    }

    if (deviceID == 0 || countryID == 0 || phoneNumber.equals("")) {
        response.setStatus(HttpServletResponse.SC_NOT_FOUND);
        return;
    }

The problem is in the line List fileItems = upload.parseRequest(request);. The returned list is empty and I can not get the form-data values.

Answer 1

It will be empty at that point if you have already (implicitly) parsed the request body beforehand. The HTTP request body can be read/parsed only once (as the client has sent it only once and won't send it multiple times).

The request body will be implicitly read/parsed when you have invoked any of the following methods before feeding the request to Commons FileUpload:

request.getParameter();
request.getParameterMap();
request.getParameterNames();
request.getParameterValues();
request.getReader();
request.getInputStream();

You need to make absolutely sure that you are not calling any of those methods beforehand (also check all servlet filters to be sure).

If you've already ensured that you aren't doing that, then the only other possible causes would be an incorrect boundary header and/or using incorrect newlines (it has really to be CR+LF and thus not alone LF). You can find a concrete and proper example at the bottom of Using java.net.URLConnection to fire and handle HTTP requests, under the section "Uploading files".