This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
Can you be more elaborate about the problem you're facing? Servlets are multi-threaded; if they were developed in a thread-safe way, then concurrent DB accesses should be no problem as far as the servlet is concerned. Or are you asking about DB issues like transaction isolation?