OSGi Basics

OSGi is specification and set of standards to develop Java based modular applications.

1. OSGi Framework : It is runtime (OSGi Container) & development environment.
2. Bundle : Basic unit to deploy into the OSGi container. It is a JAR file which contains executable code and OSGi headers in its MANIFEST.MF file.

Bundle = MANIFEST.MF + Java classes + Resources.

             a. Symantic versioning : Major . Minor . Micro - Qualifier (3.0.0-BETA).
             Eg. [1.2, 3.0) (means version 1.2 onwards and upto 3.0 not included 3.0 version)

             b. Bundle lifecycle managed by BundleActivator.

             States are :
                 1. installed (after added into the container), 2. Resolved (all imported dependencies are resolved ), 3. Starting, 4. Active, 5. Stopping, 6. Unistalling.


3. Component : It is an object (java class) which has set of functionalities. It is managed by component framework.
             Component Lifecycle : 1. active, 2. activated. 3. deactivated
4. Service : It is a component registered to OSGi Container 'service registry'.
                   Implements an interface and referenced by its interface in the OSGi Container.