This week's book giveaway is in the General Computing forum. We're giving away four copies of Arduino in Action and have Martin Evans, Joshua Noble, and Jordan Hochenbaum on-line! See this thread for details.
The Apache web service projects, SOAP and AXIS, and the Sun JWSDP are all servlet based. It your web service uses HTTP for message transport, that is the usual solution.
The servlet side then has to deal with whatever resources the particular service requires, such as databases.