+hco #15798 add missing java api for Connection.tokens

Only the `getTokens` method was missing.

Resolves #15798 

// cc @sirthias @jrudolph 
If this is a Java API, then I think it should have an explicit return type. I see that we don't have that in other places using these converters, but I think it would be good, so we don't change the API by accident by changing the converters.