Can you find all classes in a package using reflection?

Question

Is it possible to find all classes or interfaces in a given package? (Quickly looking at e.g. Package, it would seem like no.)

Answer 1

Aleksander Blomskøld's solution did not work for me for parameterized tests @RunWith(Parameterized.class) when using Maven. The tests were named correctly and also where found but not executed:

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T E S T S
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Running some.properly.named.test.run.with.maven.SomeTest
Tests run: 0, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.123 sec

A similar issue has been reported here.

In my case @Parameters is creating instances of each class in a package. The tests worked well when run locally in the IDE. However, when running Maven no classes where found with Aleksander Blomskøld's solution.

I did make it work with the following snipped which was inspired by David Pärsson's comment on Aleksander Blomskøld's answer:

Reflections reflections = new Reflections(new ConfigurationBuilder()
            .setScanners(new SubTypesScanner(false /* don't exclude Object.class */), new ResourcesScanner())
            .addUrls(ClasspathHelper.forJavaClassPath()) 
            .filterInputsBy(new FilterBuilder()
            .include(FilterBuilder.prefix(basePackage))));

Set> subTypesOf = reflections.getSubTypesOf(Object.class);