Implementing gRPC Communication

syntax = "proto3";
package shop.v1;

service OrderService {
  rpc Get(GetOrderRequest) returns (Order);
  rpc List(ListOrdersRequest) returns (stream Order);
  rpc Bulk(stream CreateOrder) returns (BulkResult);
  rpc Chat(stream Event) returns (stream Event);
}

message GetOrderRequest { string id = 1; }
message Order { string id = 1; double total = 2; OrderStatus status = 3; }
enum OrderStatus { DRAFT = 0; PAID = 1; SHIPPED = 2; }

public class OrderImpl extends OrderServiceGrpc.OrderServiceImplBase {
  @Override public void get(GetOrderRequest req, StreamObserver<Order> out) {
    Order o = repo.find(req.getId())
        .orElseThrow(() -> Status.NOT_FOUND.withDescription("order").asRuntimeException());
    out.onNext(o);
    out.onCompleted();
  }
}