This week's giveaway is in the Java/Jakarta EE forum. We're giving away four copies of Java EE 8 High Performance and have Romain Manni-Bucau on-line! See you should print out the entire stack trace instead of just the error message - then you know at which line of code the exception occurs.
Also, are you sure that in line 15 of the doPost method creating a new LoginBean object is the right thing to do? You already created one in line 8, and that one has the data which presumably is needed for retrieving the userID.