This may not be what you're after but I'll make a stab at it anyways:
Have the client save the excel spreadsheet as a *.csv file. Have a
java program that takes a *.csv file as a parameter, read each line using file io, parse each column value using StringTokenizer, then write each line to the database.
I have tried using JDBC-ODBC, to read the excel files, then update the Oracle DB but I found that setting up every client to work was more pain that it was worth. besides, the file io method was a lot faster.
Another method is to invoke SQL Loader to import the file.
All the above methods have an extra step the user has to do before the data can be written to Oracle. So this may not suit you because you don't click save from Excel.
Jamie