Part 2. Assembling components and services

Services are core to SOA. They represent functional, reusable units of code that can be combined to form applications or business processes. In chapter 1, we discussed what constitutes an ideal service, including its adherence to a well-defined service contract, as well as the fact that it’s loosely coupled, abstractly designed, and stateless (among other traits). Building such services in a way that they can be exposed through multiple protocols and languages and then distributed and administered through a service cloud can be challenging. Fortunately, the emergence of two important frameworks has greatly simplified the creation of such services: OSGi and the Service Component Architecture (SCA). OSGi, squarely aimed at Java, provides a modular framework for constructing components along with a runtime container in which they run. By itself, it doesn’t provide the features necessary for constructing SOA-ready services (that’s not its intended purpose). But this is SCA’s sweet spot.