code: @Override
      public StreamObserver<HelloRequest> lotsOfGreetings(StreamObserver<HelloReply> responseObserver) {
          return new StreamObserver<HelloRequest>() {
              final ArrayList<String> names = new ArrayList<>();
  
              @Override
              public void onNext(HelloRequest value) {
                  names.add(value.getName());
              }
  
              @Override
              public void onError(Throwable t) {
                  responseObserver.onError(t);
              }
  
              @Override
              public void onCompleted() {
                  responseObserver.onNext(buildReply(toMessage(String.join(", ", names))));
                  responseObserver.onCompleted();
              }
          };
      }
docs: Sends a {@link HelloReply} when a request has been completed with multiple {@link HelloRequest}s.