I need to develop some simple application like demo and this demo should connect to 3 clouds S3, Google Storage and Azure. This project is java based, Can I use some frameworks for it? I've looked to the jclouds, native s3 and spring data and decided to ask this question ... Thanks
JClouds would seem top be a good choice here, providing a consistent API to interact with the various cloud services. Like any abstraction, it's probably not as functional as any of the "native" APIs, but it's under very active development, so it'll improve.
I suggest you pick one and try it.