说明：  Akka Essentials is meant as a guide for architects, solution providers, consultants, engineers, and anyone planning to design and implement a distributed, concurrent application based on Akka. It will refer to easy-to-explain concept examples, as they are likely to be the best teaching aids. It will explain the logic, code, and configurations needed to build a successful, distributed, concurrent application, as well as the reason behind those decisions.include code