Why does a dependency with scope "provided" hide transitive dependencies in Maven?

Question

I have three modules in my Maven project (this is slightly simplified):

• model contains JPA annotated entity classes
• persistence instantiates an EntityManager and calls methods on it
• application creates instances of the classes in model, sets some values and passes them to persistence

model and persistence obviously depend on javax.persistence, but application shouldn't, I think.

The javax.persistence dependency is moved to a top-level POM's dependencyManagement section because it occurs in a number of submodules where I only reference that entry.

What's surprising to me is that I have to reference the dependency in application when I set its scope to provided, whereas I don't have to when its scope is compile.

With a scope of provided, if I don't list it in the dependencies for application, the build fails with an error message from javac:

com.sun.tools.javac.code.Symbol$CompletionFailure: class file for javax.persistence.InheritanceType not found

What's going on?

Answer 1

model and persistence obviously depend on javax.persistence, but application shouldn't, I think.

That's true. But transitive dependencies resolution has nothing to do with your problem (and actually, javax.persistence is provided to model and persistence on which application depends with a compile scope so it's omitted as documented in 3.4.4. Transitive Dependencies).

In my opinion, you are victim of this bug: http://bugs.sun.com/view_bug.do?bug_id=6550655

I have the same issues with an EJB3 entity that uses the Inheritance annotation: @Inheritance(strategy=InheritanceType.SINGLE_TABLE)

A client class using this entity won't compile when the ejb3 annatations are not on the classpath, but crash with the following message: com.sun.tools.javac.code.Symbol$CompletionFailure: class file for javax.persistence.InheritanceType not found

[...]

Note that is a special case of bug 6365854 (that is reported to be fixed); the problem here seems to be that the annotation is using an enum as its value.

The current workaround is to add the missing enum to the CLASSPATH.

In your case, the "less worse" way to do that would be to add javax.persistence as provided dependency to the application module. But that's a workaround to the JVM bug, application shouldn't need that dependency to compile.

Answer 2

umm, because provided dependencies are not transitive? that's builtin behavior for maven.