I recently made my first steps with Kotlin. After exploring the language for a couple of weeks, I tried to translate one of my favorite architectural patterns from my Java background to the Kotlin world - Domain Driven Design.

In my current project, we are using an event-based architecture in order to communicate between services. The events are implemented as JMS messages, which we send over ActiveMQ. Each system sends and listens to multiple events. While sending events is pretty easy, on the listener side we quickly ended up with a class explosion:

Last year, I wrote an article about generating PDFs with Java and Flying Saucer using Thymeleaf HTML templates. The article covered all basic steps to generate a simple (text only) PDF file. However, I got some comments on how to include images or how to style the PDF. So let’s have a look at part 2.

Usually, when we talk about architecture, we talk about the application itself. We think about layers, domain models and interfaces to structure our code. Most of the time the tests will follow this architecture. We create one test per service and mirror our code.

Despite a simple authentication, a lot of applications have a concept of authorisation. A user is not only logged-in, but has a set of roles which allow him to perform certain actions or see certain views. For example a user with the role ADMIN will probably be able to do more things as a user with the role CUSTOMER.

In a distributed environment, services must communicate with each other. One of the most popular ways of communication is messaging. Tools like ActiveMQ, RabbitMQ or Kafka are making it easy to exchange messages between systems. But no matter which broker you are using, you must decide which kind of message you want to send.

During the last days, I dug a little bit into the Saga pattern. The Saga pattern is an architectural pattern which provides an alternative approach to big and long-running ACID transactions. It takes a business process and breaks it down into small isolated steps - each of them with its own transaction. The overall consistency is provided by manually reverting past actions if needed (called compensating).

During the last couple of months, I wrote a lot of blog posts about ActiveMQ, AngularJS and Spring. Most of those blog posts include some small code snippets, but nothing more. That’s why I decided to make a boilerplate project to show how all those different techniques can go hand in hand in a bigger example.

Generating PDFs can be a tricky job. If you ever worked with templating engines like Jasper you probably know what I mean. On the other side, HTML makes it extremely simple to describe documents. So why not use HTML to generate PDFs?

No matter what type of software you make, there will always be errors. There might be bugs in your code or an external system is just down at the moment. No matter what, it will cause you trouble.