In this chapter, we built a simple business application that supports business-to-business transactions. We implemented a REST service in a microservices (almost) architecture using the features that are provided by the de facto standard enterprise framework: Spring. Looking back at the chapter, it is amazing how few lines of code we wrote to achieve all the functionality, and that is good. The less code we need to develop what we want, the better. This proves the power of the framework.

We discussed microservices, HTTP, REST, JSON, and how to use them using the MVC design pattern. We learned how Spring is built up, what modules are there, how dependency injection works in Spring, and we even touched a bit of AOP. This was very important because along with AOP, we discovered how Spring works using dynamic proxy objects, and this is something that is very valuable when you need to debug Spring or some other framework that uses a similar solution (and there are a few frequently used).

We started to test our code using a simple browser, but after that we realized that REST services are better tested using some professional testing tool, and for that we used soapUI and built up a simple REST test suite with REST test steps and mock services.

Having learnt all that, nothing will stop us from extending this application using very modern and advanced Java technologies, such as reflection (which we have already touched on a bit when we discussed the JDK dynamic proxy), Java streams, lambda expressions, and scripting on the server side.