5.2. OSGi Framework

The OSGi Alliance is an independent organization responsible for defining the features and capabilities of the OSGi Service Platform Release 4. The OSGi Service Platform is a set of open specifications that simplify building, deploying, and managing complex software applications.

OSGi technology is often referred to as the dynamic module system for Java. OSGi is a framework for Java that uses bundles to modularly deploy Java components and handle dependencies, versioning, classpath control, and class loading. OSGi's lifecycle management allows you to load, start, and stop bundles without shutting down the JVM.

OSGi provides the best runtime platform for Java, a superior class loading architecture, and a registry for services. Bundles can export services, run processes, and have their dependencies managed. Each bundle can have its requirements managed by the OSGi container.

JBoss Fuse uses Apache Felix as its default OSGi implementation. The framework layers form the container where you install bundles. The framework manages the installation and updating of bundles in a dynamic, scalable manner, and manages the dependencies between bundles and services.

As shown in Figure 5.1, “Red Hat JBoss Fuse Architecture”, the OSGi framework contains the following:

Each layer in the framework depends on the layer beneath it. For example, the lifecycle layer requires the module layer. The module layer can be used without the lifecycle and service layers.