Custom Log Level in Grails

Question

I want to be informed when uncaught exceptions occur in my Grails 2.2.4 application. Log4j has an SMTPAppender doing something similar, but only based on a specific log level. In my application there are already a lot of log entries in all available log levels, so sending email on ERROR or FATAL is not really an option because it would also contain non-exception entries.

Filtering uncaught exceptions in Grails is quite easy, I just redirect them to a specific controller and handle it there:

static mappings = {
    [...]
    "500"(controller: "errors", action: "serverError")
}

My plan was to introduce my own log level and use it only for uncaught exceptions. Documentation suggests this:

final Level EXCEPTION = Level.forName("EXCEPTION", 50);
logger.log(EXCEPTION, "uncaught exception", e);

But I don't know how to use this in Grails with the injected log object. It only supports the base options like log.error('foo',e). Grails documentation says how to add custom appenders, but nothing about custom levels (or did I miss it?!)

Any suggestions?

Answer 1

Grails uses Slf4j and Commons Logging to abstract the logger implementation and allow changing from Log4j to another framework without having to edit every file with a logger. Instead, the wrapper library gets the correct implementation instance based on the requested logger name and what's available from the native API. If you change implementations, the wrapper loggers work the same way as far as your app code is concerned, but they call different implementation loggers to do the actual logging.

But there's no standard between implementations for configuration, so internal Grails startup code works directly with the API to configure loggers, appenders, levels, etc. You can do the same - use the traditional Log4j logger access code to get an instance by logger name, using the same one as the preconfigured logger Grails wired up. I can never remember the naming convention for loggers in artifacts, so I cheat and add a line of code

println log.name

in a method that I know runs, and call that method indirectly via whatever controller action can get there. So for example, if I want to know the logger of FractalService, put that code in its graphJuliaSet method and call the controller action that graphs Julia Sets using this service.

Log4j loggers are singletons, if you access the logger and change it, that will affect all future calls.

So that logger is available via something like:

String name = ... // the name from the println above
Logger logger = Logger.getLogger(name)