In this chapter, we explored how to utilize Kotlin to build a Spring Boot REST application programming interface. In the process of doing so, we learned the basics of designing systems. We expressed the behavior of the messenger API system with a state diagram, and learned how to properly interpret the information represented in a state diagram. We went one step further by creating an E-R diagram to give a detailed diagrammatic representation of system entities and their relationships.
In addition, we learned how to set up PostgreSQL on a local machine and create a new PostgreSQL database. We also explored how to build a microservice with Spring Boot 2.0, connect the microservice to a database, and interact with data existing in a database with Spring Data.
Besides all this, we learned how to properly secure a RESTful Spring Boot web application with Spring Security and...