user authentication in Tomcat

I need to implement a log开发者_StackOverflowin feature for the web application that I am building on eclipse using Java EE and Tomcat, JDBCRealm has been suggested for this purpose, but I don't understand why I can't simply get the login and password and check against the database for authentication?

You can but then you are rebuilding the same functionality that is already built into JDBCRealm, you will also have user roles built into the system. Up front it will probably be easier to do your own login and password check but in the long run JDBCRealm should be more maintainable.