An OSGi Fragment Bundle is a special type of OSGi bundle that does not have its own classloader and cannot be started, stopped, or managed like a normal bundle. Instead, it attaches to a host bundle at runtime and extends its functionality.
* No Lifecycle – Fragment bundles do not have BundleActivator or lifecycle states (e.g., STARTING, ACTIVE).
* Attaches to a Host Bundle – The fragment is merged into the host bundle at runtime.
* Shares the Same Classloader – A fragment’s classes, resources, and dependencies are accessible from the host bundle.
* Cannot Be Installed/Started Independently – It must always attach to a host bundle.
* Adding Extra Resources – Useful for providing additional configuration files, images, or translations.
* Patching Existing Bundles – Enables modifying or extending an existing bundle without changing its core code.
* Providing Platform-Specific Implementations – For example, different fragments for Windows, Linux, and macOS.
* Extending Functionality – Adding additional libraries or classes to a host bundle.
MANIFEST.MF (Fragment Bundle)Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: My Fragment Bundle
Bundle-SymbolicName: com.example.fragment
Bundle-Version: 1.0.0
Fragment-Host: com.example.hostbundle # Specifies the host bundle
* The Fragment-Host header specifies the bundle to which the fragment will attach.
| Feature | Regular Bundle | Fragment Bundle |
|---|---|---|
| Lifecycle | Has STARTING, ACTIVE, etc. |
No lifecycle (merged into host) |
| Classloader | Has its own classloader | Uses host bundle’s classloader |
| Standalone Execution | Can start and stop independently | Must be attached to a host bundle |
| Use Case | Implements full functionality | Provides additional resources or patches |