This feature exists in Photoshop CS2: take a layer that has some transparency, and create a layer that will blend with it to provide effects like 'emboss' and 'inner or outer glow'.
I'd like to know how to achieve similar effects in Java2D.
I can imagine a couple of ways of how I'd start to do it, but I'd like to know if someone has an efficient way before I start.
I've looked for similar effects online, but the one at JH Labs isn't very explanatory or generic, and the one for 'Filthy Rich Clients' mentioned in another answer uses blur, and that's not generic either. The variability available to Photoshop should be in any suggestion provided as an answer to this question.