Yes, this is a manageable issue, do the following:
Store files using S3 and use an SDk for Java:
Refer this: com.amazonaws.services.s3 putObject Interface AmazonS3.
You should be able to plug the code that is used for for file saving. This should be achieveable ie: One implementation for saving the file to the local disk and another for storing it in S3. And also your startup code