Hi. Thanks for the question. I'm not sure I understand your question, but I guess you meant if you have two apps create a separate JAR containing the DTO and import it in the other two. If this is the case, the answer is: "It depends". Sometimes you can't do this, for example, if the two apps are not both part of your organization. In other cases, developers prefer avoiding to complicate the deployment (which might also make sense if there's not so much duplication) and so on. Like almost everything else in software, the right decision depends on the specific case. I hope I answered your question :)
Hi. The reason there're two services is to make the point of what a DTO is. By definition DTO = Data Transfer Object. The reason you have the "transfer" word there is because it helps transferring data between apps. Yes, of course, one can assume Postman is the other app, but to make it more realistic, I preferred to have two services. I hope it makes sense. Cheers!
Hi. No, not yet. I just answered a question asked by someone. When I'll start with the software architecture part I'll make a stream with numbered lessons so that it's easy for everyone to follow them :)
You should use meaningful names. Also, the logic should be in a service class. Regarding the package naming and the controller name, you should use nouns which are at their singular form.