Explain the OSGi lifecycle states.

OSGi Lifecycle States

The OSGi framework manages bundles through a well-defined lifecycle, allowing them to be dynamically installed, started, stopped, updated, and uninstalled at runtime.

Each OSGi bundle follows these six lifecycle states:

1. INSTALLED :

The bundle has been installed in the OSGi framework but is not yet active.
It still needs to resolve its dependencies before it can run.
If any dependencies are missing, the bundle stays in this state.

* Example : A bundle is copied into the OSGi container using installBundle("path/to/bundle.jar"), but it hasn’t started yet.

2. RESOLVED :

The bundle's dependencies are successfully resolved.
It is ready to be started.
This is a passive state—meaning the bundle is not running yet.

* Example : The framework checks and finds all required packages, so the bundle is now ready to be activated.

3. STARTING :

The bundle is in the process of starting.
The BundleActivator.start(BundleContext context) method is called.
Once the startup process is completed, it moves to the ACTIVE state.

* Example : A service registers itself in the OSGi Service Registry but isn’t fully available yet.

4. ACTIVE :

The bundle is running and fully functional.
It can now provide or consume OSGi services.
This is the main operational state.

* Example : A logging service is running and available for other bundles to use.

5. STOPPING :

The bundle is in the process of stopping.
The BundleActivator.stop(BundleContext context) method is called.
The bundle moves to the RESOLVED state after stopping completely.

* Example : A database connection bundle is closing connections before stopping.

6. UNINSTALLED :

The bundle has been removed from the system.
It cannot be resolved or started again unless reinstalled.

* Example : An old version of a logging bundle is removed and replaced with a newer version.

OSGi Lifecycle State Transitions

Here’s a simplified flowchart of the OSGi lifecycle:

[INSTALLED] → (Dependencies resolved) → [RESOLVED]  
[RESOLVED] → (Start command) → [STARTING] → [ACTIVE]  
[ACTIVE] → (Stop command) → [STOPPING] → [RESOLVED]  
[RESOLVED] → (Uninstall command) → [UNINSTALLED]

Managing OSGi Lifecycle Using Code :

Bundle bundle = bundleContext.installBundle("file:mybundle.jar");  // Install
bundle.start();  // Moves to ACTIVE state
bundle.stop();   // Moves to RESOLVED state
bundle.uninstall();  // Moves to UNINSTALLED state