• grails
• logging

To turn on display of debug log messages in Grails 1.0.2, add this to the bottom of grails-app/conf/Config.groovy:

environments {
  development {
    log4j {
      logger {
         grails."app"="debug,stdout"
         //grails="debug,stdout"    // maybe need this too
      }
    }
  }
}

Info on other versions continues below.

With Grails 1.0.3 and 1.0.4, the above will produce an error message like No such property: context for class: java.lang.String

For 1.0.3 and 1.0.4, use this:

environments {
  development {
    log4j {
      logger {
        grails {
          app="debug"
        }
      }
    }
  }
}

In your code, simply use log.debug("my message")

Thanks to the grails-user mailing list for a clue towards this.

Update: I've been working through all this again for 1.0.4 and 1.1. I added a commented line for 1.0.2 that I'm now needing to include, although it unfortunately doubles the output.

Unfortunately, the 1.0.3/4 method does not work in 1.1. After upgrading, you need to change the extra logging snippet even if you leave the standard logging section in the old format. For 1.1:

environments {
  development {
    log4j = {
      debug 'grails.app'
    }
  }
}

Also note that one could add the grails.app config lines in the middle of the regular log4j configuration section, but the examples given illustrate how to have different log levels in different environments, e.g. debug messages in development mode and only error messages in production.