Representational state transfer (REST) is a style of designing loosely coupled applications that rely on named resources rather than messages. The hardest part of building a RESTful application is deciding on the resources you want to expose. Once you’ve done that, using the open source Restlet framework makes building RESTful Web services a snap. This tutorial guides you step-by-step through the fundamental concepts of REST and building applications with Restlets.
Este tutorial é muito simples e dá pra entender bem o conceito e implementação de RESTful Web service em Java. Eu completei ele e teste no WebSphere Community Edition.
Para ver mais teoria começe por http://en.wikipedia.org/wiki/REST
E depois veja mais tutoriais no DeveloperWorks:
- Write REST services
- Ajax and REST, Part 1
- Create a photo album application with Project Zero and REST design principles