java- apache http client-query regarding submission of files as part of a multi part post request

Question

I am trying to use the latest Apache HTTP Client (v4.x) to send a multi part POST request- the example code provided with the docs gives the following code sample (somewhat modified) to make a POST request--

        FileBody bin = new FileBody(new File(args[0]));
        StringBody comment = new StringBody("A binary file of some kind");
        MultipartEntity reqEntity = new MultipartEntity();
        reqEntity.addPart("bin", bin);
        reqEntity.addPart("comment", comment);
        httppost.setEntity(reqEntity);

What I am confused about is, if I have multiple files to be added, then in the code

   reqEntity.addPart("bin", bin);

what does the first string represent? Is it the name of the file which is being sent as part of multi part post?

Answer 1

Multipart Form requests can have several parts, and each part is given a name (similar to a regular form request). This name can be used on the server side to retrieve a specific part, given the name. Good details are available in RFC 2388:

    3. Definition of multipart/form-data

       The media-type multipart/form-data follows the rules of all multipart
       MIME data streams as outlined in [RFC 2046].  In forms, there are a
       series of fields to be supplied by the user who fills out the form.
       Each field has a name. Within a given form, the names are unique.

       "multipart/form-data" contains a series of parts. Each part is
       expected to contain a content-disposition header [RFC 2183] where the
       disposition type is "form-data", and where the disposition contains
       an (additional) parameter of "name", where the value of that
       parameter is the original field name in the form. For example, a part
       might contain a header:

            Content-Disposition: form-data; name="user"