[Hawkular-dev] logging notes from call

[John Mazzitelli]

Here's the notes from our call this morning regarding the use of jboss logging - chime in if I got something wrong, or if you disagree (say, for example, we should use some other third party logging framework rather than JBoss Logging :-)

Here's an example from Undertow:

https://github.com/undertow-io/undertow/blob/master/core/src/main/java/io/undertow/websockets/core/WebSocketLogger.java

We agreed that Hawkular will not use this mechanism for DEBUG or TRACE level messages, but will use it for INFO, WARN, ERROR, and FATAL.

In our message interfaces, we can do what undertow does - that is, declare the logger instance right in the interface, for example, put this in your MsgLogger interface:

   MsgLogger LOGGER = Logger.getMessageLogger(MsgLogger.class, MsgLogger.class.getPackage().getName());

Each major component will have its own logging prefix (alerts will have, for example, "HAWKALRT" or whatever they want to call it; metrics will have "HAWK-METRICS" or whatever; inventory another like "HAWKINV"). Each major component will then divy up the ID ranges how it sees fit.

It is most likely useful to have one logging interface per maven module within the major component; however, this is up to the developers how they want to separate or combine their messages - one uber interface or one per maven module or something else. but just keep in mind the pros and cons of each (e.g. if you have one uber interface, all of your maven modules will have a dependency on it - and if you add a message, all maven modules that depend on it will need to rebuild with it, even if they don't need the message - plus, all your developers will need to edit the same file throughout development, so there will be alot of git pulling, merging, and conflict resolutions).

Note that in my work, I put one message interface in each maven module that needs messages. I put them in a package called .log and I named them all "MsgLogger". I don't know if its the right thing to do to name them all the same - but having the package names differentiate them was all I needed so far to be able to find them when I needed to edit them in Eclipse (I just searched for "MsgLogger" and I got the full list of all my message loggers in the search window - each for me to pick which one I wanted). Again, time will tell if I should have named them differently rather than all the same - I really don't have an opinion either way. I don't have good argument for naming them the same OR naming them differently. Up to you what to do.

To log ad-hoc messages in the debug and trace level, you'll need to define a JBoss Logging Logger like this:

   private final Logger log = Logger.getLogger(YourClass.class);

and use debugf to log debug messages as an example:

   log.debugf("This is the first arg [%d] and this is the second [%s].", myNum, myStr);

We are hopefully going to have the parent pom declare the logging processor for us, so you only should have to declare logging deps in your maven modules, and the log code generation will just work. You need these two deps:

<dependency>
  <groupId>org.jboss.logging</groupId>
  <artifactId>jboss-logging</artifactId>
</dependency>

<dependency>
  <groupId>org.jboss.logging</groupId>
  <artifactId>jboss-logging-annotations</artifactId>
  <scope>provided</scope>
</dependency>