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From "Bob Glamm (JIRA)" <j...@apache.org>
Subject [jira] Created: (WW-3526) Augment JakartaMultiPartRequest to include optional progress listener
Date Tue, 02 Nov 2010 20:52:24 GMT
Augment JakartaMultiPartRequest to include optional progress listener
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                 Key: WW-3526
                 URL: https://issues.apache.org/jira/browse/WW-3526
             Project: Struts 2
          Issue Type: New Feature
          Components: Dispatch Filter
    Affects Versions: Future
         Environment: N/A
            Reporter: Bob Glamm
            Priority: Minor
             Fix For: Future


Original concept from David Casserly: see http://www.devedup.com/ajaxfileupload/

The basic idea is to augment JakartaMultiPartRequest to allow users to specify a file upload
progress listener (see Commons FileUpload ServletFileUpload.setProgressListener()).  The original
concept by Casserly references a specific ProgressMonitor class that implements FileUpload's
ProgressListener interface.  I'd propose an alternate solution: allow the user to configure
the fully-qualified name of an optional listener class via @Inject("struts.multipart.monitor"),
then:

  o  require the listener class to also implement an interface that specifies public void
abort(); as its only method;
  o  in JakartaMultiPartRequest.parseRequest(), attempting to instantiate the specified listener
class via Class.forName().newInstance();
  o  store the instantiated listener in the session, as per Casserly's example;
  o  in JakartaMultiPartRequest.parse(), in the catch(FileUploadException) block, calling
the abort() method on the listener class if it is in the session.

Users can then implement an action that retrieves the upload status (via AJAX or some other
mechanism) by retrieving their listener object from the session (as per Casserly's example.)
 AJAX retrieval allows implementation of file upload progress bars, a la GMail's attachment
upload mechanism.

One possible issue I see with this is: what happens if multiple file upload requests happen
simultaneously for a user session?

I have a partial implementation but I'm not familiar with the Struts development process or
philosophies, so I'm throwing this out there for review.  If there are better ways to do this,
let me know.  I can (eventually) provide a patch to 2.2.1 or HEAD with a little assistance,
I think.

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