Try Murach's servlets and JSPs 2nd Edition. The book is structured in a way thats easy and straight-forward with complete good practical examples. Considering you are coming from the 'Head First Servlets & JSPs' the Murach book will be walk-over. Where as HF servlets & JSPs focusses mostly on certification objectives Murach ventures into getting you practical insight on topics not necessarily on the exam but useful in development. Thus said Murach is only a beginner's guide and most probably you would still need other reference materials to grow further.