How can I get annotations on rpc method being called in grpc-java

I need to validate request before different rpc methods being called with different validators.

So I implemented validators like

class BarRequestValidator {
    public FooServiceError validate(BarRequest request) {
        if (request.bar.length > 12) {
            return FooServiceError.BAR_TOO_LONG;
        } else {
            return null;
        }
    }
}

and add a custom annotation before my rpc method

class FooService extends FooServiceGrpc.FooServiceImplBase {
    @Validated(validator = BarRequestValidator.class)
    public void bar(BarRequest request, StreamObserver<BarResponse> responseObserver) {
        // Validator should be executed before this line, and returns error once validation fails.
        assert(request.bar <= 12);
    }
}

But I found that I can't find a way to get annotation information in gRPC ServerInterceptor. Is there any way to implement grpc request validation like this?