Java - Managing multiple asynchronous servlet requests and placing them in a queue to perform tasks

I'm using a Bootstrap Krajee FileInput widget on a webpage. Hundreds of photos are uploaded to the server through this widget and they are all sent individually as a set of asynchronous calls. The issue is that our server is having difficulty handling hundreds of photos at once. It isn't a network issue. I'm leaning more toward it being a file IO/database performance issue.

I need a way to put these photos all into one queue on the server side and then pop them off, do the work, and send a JSON response back with the servlet.

Can anyone point me to a pattern (or implementation of a pattern that would work well here? Am I completely off base?

I included a quick drawing illustrating what I think should happen.

drawing