Images Service on GAEJ provides the ability to manipulate images, thus you can composite multiple images into a single one. I'll use this possibility to display a graphical hit counter. This tutorial is only a kind of how-to. I'm sure you can write real programs using the instructions given in this post. For simplicity reasons error handling are reduced to the minimum.
The idea is pretty simple, persist a counter using Memcache or DataStore, have digits from 0 to 9 as PNG images, read images as bytes, make images and composites of these images, put all composites in a List and finally use this List to get the composed image.
Java, JEE, JavaFx and more: A graphical counter on GAEJ (Google App Engine for Java) using Images API Service