Finding a type in the classpath of an Eclipse Java project

Recently, I started to contribute and maintain Pitclipse, an Eclipse plugin for running mutation testing with PIT.

We needed a mechanism to detect whether JUnit 5 is in the classpath of a Java project (so that we could run PIT with its JUnit 5 plugin).

The first implementation of such a mechanism was rather cumbersome since it manually inspected the Java project’s classpath entries. Something like that:

That’s rather unclear, and there are lots of paths to test.

I opened an issue for investigating an alternative implementation,, and I was thinking of something simpler, along these lines:

We could try to load some classes of the JUnit 5 engine by constructing a classloader using the classpath of the Java project.
Something like (untested):

That’s simpler and cleaner, but we can do better than that 🙂

JDT provides a lot of API for such things. For what we need to do, we can simply rely on IJavaProject method findType:

IType findType(String fullyQualifiedName)
Returns the first type (excluding secondary types) found following this project’s classpath with the given fully qualified name or null if none is found.

So it’s just a matter of creating a reusable method, e.g.,

And we can simply call it by specifying the fully qualified name of a type that we know belongs to JUnit 5 (PR

Now we don’t even have to test several cases: we simply rely on the correctness of the implementation of findType. This is expected to work on Java projects, Maven projects, Gradle projects, etc.

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