I created multiple custom Exceptions for various Errors that could occur during runtime. For this I'm using the @ControllerAdvice annotation and a global error handler (as described here:

You can use below code to loop through to get the root cause of exception.

public static Throwable getRootException(Throwable exception){
         Throwable rootException=exception;
         while(rootException.getCause()!=null){
          rootException = rootException.getCause();
         }
         return rootException;
        } 

So in essence you need to get the root cause of your exception in the exception handler and build appropriate response for your clients.