How to include a dependency to a jar file from an eclipse/osgi application?
eclipse, eclipse-plugin, java, osgi, plugins
Solution
For the runtime it is always the Manifest and the headers there that control what is in your bundle classpath. There are three ways to get access to a jar:
Import-Package header. This is the recommended way. You define one import per package you need. You jar you want to access has to be deployed in the runtime as a bundle. It also needs to export all needed packages.
Require-Bundle . This is another way to access bundles. You define the id of the bundle you need and see all packages it exports. As Require-Bundle binds you more closely to the other bundle the Import-Package way should be preferred.
Bundle-Classpath . This allows to add jars to your classpath that you embed into your own bundle. This should only be a last resort when the other way do not work. You can have nasty classloading issues when mixing this with the other methods.
You can find many pre built bundles in maven central. Many jars today already contain an OSGi manifest. For the cases where this is not true many jars are repackaged as bundles by servicemix. See groupId: org.apache.servicemix.bundles. There is also the spring bundle repository where you find some more.
Below I listed some resources you might want to read:
http://www.aqute.biz/Blog/2007-02-19
http://wiki.osgi.org/wiki/Import-Package
http://wiki.osgi.org/wiki/Require-Bundle
http://www.vogella.com/blog/2009/03/27/required-bundle-import-package/
Problem
I created an Eclipse 4 application and I needed a `jar` offering a functionality as part of my application (this could be anything e.g. `log4j` to make it trivial). I added the `jar` as part of my project's classpath (`Right Click->Configure Build Path`) but on runtime my service failed with a `ClassNotFound` error (from OSGI I guess?). Anyway searching this it turned out, at least as I have understand it, that I should add the jar as part of another `Plugin` and create a dependency from my application/service to this new plugin. I.e. I created a `Plugin Project from Existing JAR archives`. This time the setup worked. So if I understand this, when developing for Eclipse/OSGi we should not add `jars` in the classpaths directly but add them via plugins (why?). Question: If I am correct so far, what is the standard practice to include `jars` when developing a project? Define/Create one `Plugin Project from existing JAR archives` and add all the required third party libraries needed there, or have a different plugin project per needed `jar` or something else perhaps??? Sorry if my terminology is not accurate. I am new in OSGi and Eclipse programming Note: When talking about `jars` I am not refering to other OSGi services. I am refering to the norm of using ready, reliable third party libraries that would be needed by many parts of an application. E.g. `log4j` or an xml parsing library or `apache commons` etc