With a requirement as vague as that, this is about the best I can come up with.
1. Learn java, Struts, Hibernate, SFTP for encrypted file transfer,GNU Privacy Guard (GPG) for Decryption/Encryption and postgre
2. Write code.
3. Create executable jar file.
4.
Test
5. Repeat 2, 3 and 4 until program works
6. Package jar file and any required third party stuff
7. Send to client.