Logging Still Sucks

March 7, 2013

It's 2013, and for some reason logging is still a pain in the ass when you use Java (SLF4J) or .NET (log4net).

SLF4J is indeed a better version of JCL. Using an abstraction library is indeed better than just choosing a logging framework outright. I can agree with that. But in my opinion there is still something wrong with the programming model:

  • Your DEBUG is not my DEBUG: choosing a log level is highly subjective. Most projects don't have a standard practice for this, so everything just becomes a dumping ground. All you can say is that DEBUG will probably be more verbose than INFO. As a wise man once said: enabling log levels is like a box of chocolates.
  • Designed to be an afterthought: it's too easy to ignore SLF4J and then start using it when you're already in production. Logging is actually a feature of the library you are using, but nobody will even realise it's there until they have problem. Problem in production? Let's turn up logging! However, this can have side effects in terms of triggering suble bugs and degrading performance. Now you have two problems in production.
  • Simple case is no longer simple: FFS, just let me dump this thing to sysout so I can move on with my life.

See the trend here? Only the API consumer knows what your DEBUG means for their DEBUG. Also they need to know logging could be happening in the first place. They need to take the time and map your logging to their logging (if they want to) and make sure that everything still works as expected with logging enabled. So as a API author, what do you do? You write an API.

  public interface FooLogger {
    void FYI(Event event);
    void WTF(Event event);
    void OMG(Event event);

So then as an API consumer, I implement FooLogger and give it to the API:

  class MyFooLogger implements FooLogger {

    public void FYI(Event event) {
    public void WTF(Event event) {
    public void OMG(Event event) {

  Library lib = Library.Create(new MyFooLogger());

An example of this style can actually be found in the Apache Velocity project. For some reason the SLF4J guys don't like this:

It is reasonable to assume that in most projects Wombat will be one dependency among many. If each library had its own logging wrapper, then each wrapper would presumably need to be configured separately. Thus, instead of having to deal with one logging framework, namely SLF4J, the user of Wombat would have to detail with Wombat's logging wrapper as well. The problem will be compounded by each framework that comes up with its own wrapper in order to make SLF4J optional. (Configuring or dealing with the intricacies of five different logging wrappers is not exactly exciting nor endearing.)
I don't see the problem. You write the connector code once for the lifetime of a project. This code could last for years. The code will be simple as it will be specific to your use case (e.g. log to an existing NoSQL system). You choose when you do it. And seriously, if the framework makes this difficult then you are essentially admitting their API sucks. Nothing more.