What is the purpose of the MANIFEST.MF file in an OSGi bundle?

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In an OSGi bundle, the MANIFEST.MF file, located in the META-INF directory, serves as a crucial descriptor that provides essential metadata about the bundle. Its primary purpose is to enable the OSGi framework to:

Understand the bundle's contents :
- It defines the bundle's identity, dependencies, and exported packages.
Manage the bundle's lifecycle :
- It provides information that the framework uses to install, resolve, start, stop, and uninstall the bundle.
Handle dependencies :
- It declares the Java packages that the bundle imports from other bundles, as well as the packages that it exports for other bundles to use.

Here's a breakdown of key functions :

Identifying the Bundle :
- Bundle-SymbolicName: Uniquely identifies the bundle.
- Bundle-Version: Specifies the bundle's version.
Managing Dependencies:
- Import-Package: Lists the packages that the bundle requires from other bundles.
- Export-Package: Lists the packages that the bundle makes available to other bundles.
Controlling Bundle Behavior:
- Bundle-Activator: Specifies the Java class that the framework should use to start and stop the bundle.
Other Metadata:
- The manifest can also contain other metadata, such as information about the bundle's class path, and other custom headers.

In essence, the MANIFEST.MF file is the cornerstone of OSGi's modularity, enabling the framework to dynamically manage and connect bundles.