2.7. OSGi dependency resolution

You’ve learned how to describe the internal code composing the bundles with Bundle-ClassPath, expose internal code for sharing with Export-Package, and declare dependencies on external code with Import-Package. Although we hinted at how the OSGi framework uses the exports from one bundle to satisfy the imports of another, we didn’t go into detail. The Export-Package and Import-Package metadata declarations included in bundle manifests form the backbone of the OSGi bundle dependency model, which is predicated on package sharing among bundles.

In this section, we’ll explain how OSGi resolves bundle package dependencies and ensures package consistency among bundles. After this section, you’ll have a clear understanding of how bundle modularity metadata is used by the OSGi framework. You may wonder why this is necessary, because bundle resolution seems like an OSGi framework implementation detail. Admittedly, this section covers some of the more complex details of the OSGi specification; but it’s helpful when defining bundle metadata if you understand a little of what’s going on behind the scenes. Further, this information can come in handy when you’re debugging OSGi-based applications. Let’s get started.