Hi Chandra,
I'll be a bit intrusive, but you dont want to run the wdj in the background.. you actually need to do something that is inside the wdj execute when you login.
First, you need to get the functionally or business logic out of wdj into a more suitable jee technology (perhaps a mbean or ejb) and trigger a scheduled task uppon login.
Hope this helps to clarify your actual requirement
D.