The next steps showed how to improve the design through successive refactoring: first separating each technical concern as a standalone verticle, then extracting Vert.x services for API cleanliness and finally introducing JUnit tests for asynchronous code.

We then ventured into consuming third-party HTTP/JSON services using the web client API that further simplifies the usage of the HTTP client from Vert.x core. Conversely, we also saw how to expose HTTP/JSON web APIs with the elegant Vert.x web module.

The Vert.x core API relies on callbacks as it is the most generic way of processing asynchronous events. Vert.x provides a simple promise / future API. While Vert.x futures are composable, they shall be confined to limited usages such as dealing with verticle deployments and initialization. We saw how RxJava is supported in Vert.x, and we encourage you to use it for your own verticles. What’s more RxJava is the most popular reactive programming library on the JVM, so you will easily find third-party libraries to integrate consistently in your end-to-end reactive applications.

Modern web applications tend to have the server expose just HTTP/JSON APIs, and rely on client-side web frameworks for the user interface. We saw how to do that with AngularJS so as to turn our wiki into a single-page application.