Your web.xml isn't valid, but I assume that's a copy-paste error.
The problem is in the method signatures of doGet() and doPost().
You've reversed the order of the parameters. That means that these methods are not valid overrides.
If you annotate methods that are supposed to override a method of a superclass, you should always add the @Override annotation.
It will help you catch stuff like this really easily at compile time
Build a man a fire, and he'll be warm for a day. Set a man on fire, and he'll be warm for the rest of his life.