在app引擎中上传图像和使用getServingUrl（）的正确流程是什么？

I have an android app that wants to include image sending in the instant messaging client. I'm terribly confused on the way to do this using the blobstore or google cloud storage. Can someone please outline the steps to achieve this from the backend perspective? My goal is to end up using getServingUrl and have an external url for the app to hit and get the image. I'm using java and google cloud endpoints.I have an android app that wants to include ima