Question

There are two main approaches when developing an OSGi application with Maven: POM-first and MANIFEST first.

I’m looking for an answer that is in a form of a table that shows pros and cons of each method.

To be more specific, I would also like to know how it relates to:

• Maturity of toolset
• Vendor independence
• Development ease (which includes finding people who can do the development on the tooling)
• Compatibility
• Avoiding ClassNotFound
• Avoiding manual work

Answer 1

At present this is what I can come up with

POM-First Pros (using maven-bundle-plugin)

• Leverages existing Maven skills, repositories and tooling.
• Likely easier to find people who know how to manage pom.xml rather than MANIFEST.MF along with pom.xml
• Most of the information in MANIFEST.MF can be obtained from the pom.xml itself.
• Can work with other IDEs not just Eclipse based ones.
• Less invasive, just add the single plugin and change the packaging type to “bundle”

POM-First Cons

• ClassNotFoundException more likely to occur at runtime. However, this can be mitigated using pax-exam (although it is very complicated to set up).
• Still need to understand how the MANIFEST is setup to make sure the instructions configuration element is set correctly.

MANIFEST-first Pros (using tycho-maven-plugin)

• Seems to be the recommended approach, or at least talked about as the recommended approach, but I can’t really see why it has significant benefit. (Hence why this question was asked).
• Good for developing Eclipse plugins and integrates well with PDE
• Provides tooling for testing thus allowing ClassNotFoundException to appear during JUnit testing rather than runtime.

MANIFEST-first Cons

• Seems to only work well on Eclipse based IDEs. You don’t have to use Eclipse, but without the PDE would you want to?
• Violates DRY principles since I have to do put keep the names and versions from the POM and MANIFEST.MF in sync.
• Need to name things in a specific fashion
• You cannot mix, meaning existing Maven multi-project installations cannot just tack on OSGi support
• A lot more configuration compared to maven-bundle-plugin is needed to get less warnings: http://wiki.eclipse.org/Tycho/Reference_Card#Examplary_parent_POM
• Have to make test cases a separate project. It won’t run when built in src/test/java.
• Seems that it will only test classes that are exposed, in other words those in “.internal.” is not testable.

If I were asked for a recommendation for an enterprise that is using Maven already and want to move to OSGi then it would be POM first

If I were asked for a recommendation for someone who is doing Eclipse plugin development, then it is Manifest first — with tycho