Frequently Asked Questions

Should a bundle import its own exported packages?

In OSGi R3 this was always the case, since Export-Package implied Import-Package. It was a good idea then and is generally a good idea now.

The whole point is substitutability of providers.

If you import the packages you export, then the framework is free to choose a different provider of those packages for your bundle at resolve time, which means that your exports may go unused. However, this is a good thing, because the framework tries to minimize the number of active versions of a given package. The reason why this is a good thing is because it allows for higher levels of bundle interoperability. The more versions of a given package that are in use at any given time can lead to conflicts when trying to resolve bundle package dependencies and this also leads to partitioning of the service registry, since bundles can only see a single version of a given service package.

If your bundle only exports its packages, then it is forcing the framework to wire itself to its own version, which can result in more active version of the given package.

The main time you want to export only, is if your bundle is purely a library bundle, then its packages will only be used if they are needed. Another case might be if you have tightly coupled bundles sharing implementation packages. However, if your bundle will be started and especially if the exported packages define service interfaces or are referenced from service interfaces, then you will generally want to export and import them.