For some reason one common request we see on OTN, especially from people who just start their JDev/ADF route from Oracle Forms background, is to create a login screen that uses a database table with username/password to validate users.
It might be that this is the way people managed users in their Forms application.
Now in reality this is not the way they'll probably end up doing authentication in their ADF application - after all ADF and Java EE has a complete security framework for this.
But never the less many people want to try it that way.
So I quickly created a simple sample using basic JSF page flow a login page and a login button on it that just uses JDBC to query for the existence of a username in the employees table.
You can download the sample from here
Check out the GetUser.java file for the code I use and modify your DB connection and query as needed and then run the getUser.jspx file.