Rethinking logging on the JVM with Logoon

Logging has been around on the JVM for a while now. It all started with Log4J back in 2001. Log4J was the first logging framework and it is still around today (in its version 2). It provides a simple and efficient API (compare to System.out.println that was in use before).

  1. Get a logger for a class
  2. Use that logger to log messages
val logger = Logger.getLogger(classOf[MyClass])
...
logger.log(Level.DEBUG, "I am doing something right now")
...
logger.error("Oops, something went wrong", theException)
...

Today there are a few more frameworks on the JVM but they all provide similar APIs as Log4J:

  • JUL(2002): java.util.logging provides a standardisation of Log4J and of course provides a similar API
  • Commons-logging (2002): Apache project providing a façade over Log4J, JUL, … still the same API
  • SLF4J (2005): Another façade over Log4J (1&2), JUL, JCL, … no much changes in the API
  • Logback (2006): Brings structured logging with an API compatible (and similar) to SLF4J (and Log4J)
  • Log4J2 (2012): Rewrite of Log4J inspired by Log4J and Logback with improved performances. The API does not change much though.

As you can see the logging APIs available on the JVM haven’t changed much over the last 15 years. The most interesting additions are structured logging and the Mapped Dependent Context (MDC) as we shall see later.

In this post I am going to look at the current limitations of these APIs and see how we can overcome them while still relying on this frameworks to actually write the logs. Continue reading “Rethinking logging on the JVM with Logoon”

Fluent – A deep dive into Shapeless and implicit resolution

As promised in my previous post we’re going to explore to internal of Fluent and how it uses Shapeless and implicit resolution to transform case classes.

Fluent started as an experiment (and still is), the code is rather small (about 300 lines of code) and yet I am still impressed by the variety of cases it can handle.

Before working with Shapeless I’ve often heard that is pure magic and I got the impression that most people (including me) don’t really know how it works. It turns out that the principles used in Shapeless are not really difficult to understand – especially if you read the well-written Type Astronaut’s guide to Shapeless.

Understanding how Shapeless works doesn’t mean it’s easy to work with. Actually Shapeless makes a heavy use of implicits and working with implicits is hard. Remember that implicits resolution is performed at compile time so when it fails, there is nothing to debug, no log messages or stack trace. We are just left with rather blunt messages like could not find implicit value for parameter ...

In this post I am going to explain the concept used in Fluent, the problem I faced during implementation and hopefully by the end of the post, you’ll know enough to understand and edit the code (Pull requests welcomed!). Continue reading “Fluent – A deep dive into Shapeless and implicit resolution”

Introducing Fluent – the seamless translation layer

In Domain Driven Design (DDD) it is recommended to introduce a translation layer (aka anticorruption layer) between 2 bounded contexts. The role of the anticorruption layer is to avoid any concepts to leak from one domain into the other.

This is a sound idea as it keeps the domains isolated from each other ensuring they can evolve independently. After having implemented several anticorruption layers I realised that, although useful, they also introduced a lot of boilerplate code that doesn’t add much value to the business.

To this extent, let me introduce Fluent, a library that aims at getting rid of this boilerplate code by leveraging all the power of Shapeless and its generic programming. Continue reading “Introducing Fluent – the seamless translation layer”