classOf T instead of T$ for Java library that does reflection

Question

I'm using Scala with a Java library that expects to be passed a class with a public static void main(java.lang.String[]) so it can run call it via reflection for integration tests.

object RestServer {
    def main(args: Array[String]): Unit = { /* run the server */ }
}

Due to the behavior described in this answer to another question, this gets compiled to two classes.

public final class com.example.RestServer$ {
  public static final com.example.RestServer$ MODULE$;
  public static {};
  public void main(java.lang.String[]);
}

and

public final class com.example.RestServer {
  public static void main(java.lang.String[]);
}

When I pass the class to the library

@IntegrationTest(main = classOf[RestServer.type])
class MyTests extends RapidoidIntegrationTest { }

I'm actually passing the object singleton instance (RestServer$), not the RestServer class that has the static void main() method.

This wouldn't be a problem, except the library verifies that the method it is calling is both public and static before calling it?

How can I get the RestServer class instead?

@MateuszKubuszok `classOf[RestServer]` doesn't compile. `not found: type RestServer` — RubberDuck, Feb 15 '21 at 16:03
Is it an option that you define an empty companion class `RestServer`? Otherwise I think you are stuck. — Jasper-M, Feb 16 '21 at 13:02
@Jasper-M that's an option, yes, but I don't understand how that helps. I'm more of a CLR than a JVM guy. — RubberDuck, Feb 16 '21 at 13:51
Then you can use `classOf[RestServer]`, because then the class `RestServer` "exists" to Scala. — Jasper-M, Feb 16 '21 at 14:38

score 1 · Accepted Answer · answered Feb 16 '21 at 20:18

If you have control over the RestServer source file you can add an empty companion class.

object RestServer {
    def main(args: Array[String]): Unit = { /* run the server */ }
}

class RestServer

That way Scala will recognize that a class RestServer exists, so classOf[RestServer] will compile and give you the class that contains the static method.

classOf T instead of T$ for Java library that does reflection

1 Answers1