Batch Command Processor

Question

I have a page that needs to handle updates to multiple recordsets. Each of these updates takes roughly 3 seconds to do. Therefore, we want to present a progress bar to the user so they know how close they are to being done. The progress bar is in a popup window.
My idea is, make a stack of "Command" classes with a ".execute" method, pass the stack to the page, pop off the first element, run .execute, write my progress bar, submit to myself thereby passing the updated stack, and when there aren't any more elements on the stack, I'm done. Cool. Very low coupling. Very reusable.
The problem is that I can't pass objects through forms. I would need to use a session scope bean to keep that stack of objects around. The problem with this is that if the user closes the window in the middle of the process, the stack is left hanging around since the user only closed the popup, and didn't end their session. Then, next time the user went to do this, I have all these old commands trying to be executed.
What would be IDEAL, is if I could pass an object through the request on the backend. Unless this is possible, however, I think I'm going to have to do something like serialize my object and put it as the value in a hidden input. However, I have no idea how this works.
So, in order of descending idyllity (??):
1) If anyone knows how to pass an object through a form, much obliged.
2) If anyone knows an easy way to use serialized objects in forms, coo.
3) If anyone has a better solution to this problem, fantastic.
4) ANY WAY to keep objects between requests besides session.

Answer 1

Here is how I would handle the situation.
Use Sesssion, but reference the complete transaction by a unique identifier.
long batchId;
if ( request.getParameter( "BATCH_ID" ) == null )
  //create new batch transaction id
  batchId = (new java.util.Date()).getTime();
} else {
  //Must be second or third update so read batch Id from client
  batchId = Long.parseLong(request.getParameter "BATCH_ID" ) ).longValue();
Stack myCmds;
if ( session.getValue( "BATCH_ID_" + batchId ) == null )
   //create your Stack Object & dump to session
   myCmds = getCommandStack();
   session.putValue( "BATCH_ID_" + batchId , myCmds );
} else {
   //retrieve obj from session
   myCmds = (Stack)session.getValue( "BATCH_ID_" + batchId );
}Make sure you print back to the client a hidden field called BATCH_ID with the batchId;
With this model, if a user closes the window in the middle of the batch update, they will lose their batchId, since the only place it is stored is in client html. Because they have lost their batchId, when they attempt to start again, they will receive a new batchId and a new Command stack.
let me know if this makes sense
I think this satisfies your requirements, and it also utilizes the preferred way to store temporary objects between asynchronis client requests.