Well, I don’t know Java or JCO, and I can’t tell from your code what RFC you’re using, but I can say this:
1) A structure is a temporary work area (a record layout), and
2) A structure can be loaded to an “internal” table, which is also a temporary work area, and is not a database table.
It sounds like your structure is being loaded to an internal table. Loading a structure (or internal table) does not automatically load a related database table. You need a second routine (RFC or BAPI) to move the data from the structure (or internal table) to the database table. Perhaps your SAP colleague can help you identify the required routine. Good luck.