Its as simple as this:
Step 1: The end-user submits his file to your system (for how to upload a file in
Java you can find lots of examples on Google).
Step 2: You can use your File Api to store/refer/delete that file on your server at the same time store the path of the file in your database column.
and when the user want to retrieve it you are now referring to the file in your server not in the end user machine.
As Tim and William said it is not advisable to store entire file in the database.