As explained before you will have to parse the data from the POST method to reconstruct the file. The format of file is irrelevant, the program you write should reconstruct whatever the file was originally.
What you need to do now is:
1 Create an HTML form that uses the post method as described by another user in your previous post.
2 Write a servlet to parse and reconstruct the file on your SERVER.
3 Once the file is reconstructed you can save it to file on the server, or put it into a database.
These are the steps you must take, you cannot simply 'attach' a file, this is not E-mail!
You send a data stream to the server, you need to convert this back to file.