AppEngineFile file = fileService.getBlobFile(blobKey);
FileReadChannel ch = fileService.openReadChannel(file, true);
ByteBuffer dst = ByteBuffer.allocate((int)blobInfo.getSize());
try {
	int sum=0;
	while (true) {
		int read = ch.read(dst);
		sum+=read;
		System.out.println(sum+" "+read);
		if (read<0) break;
	}
} finally {ch.close();}