Create a new user account for your MySQL DB which only has INSERT
priviliges into your table. Have your Java program use that password.

   Now people can insert into your DB, but they can't delete or do other
stuff to it.

   You'll still be vulnerable to DOS (Denial of Service) attacks in which a
malicious user tries to make a billion inserts into your table, but I think
it's impossible to avoid that. At best, you could add an extra processing
layer between the DB (e.g. a WebService), which checks against duplicate
entries, or flooding from a single IP address or something like that.

   - Oliver