OSGi is a Java-based framework for creating applications as a set of interconnected modules. OSGi lets you install, start, stop, update, or uninstall modules at execution time without taking down your entire system. It's the backbone of the Eclipse plugin system, as well as many Java EE containers, such as GlassFish, Geronimo, and WebSphere.
OSGi in Action provides a clear introduction to OSGi concepts with examples that are relevant both for architects and developers. You'll start with the central ideas of OSGi: bundles, module lifecycles, and interaction among application components. With the core concepts well in hand, you'll explore numerous application scenarios and techniques. You'll learn how to migrate legacy systems to OSGi and how to test, debug, and manage applications.