logger-category-inheritance.md

Logger Category Inheritance

We have a convention for our category names where each category name uses dot-notation according to the components path. Using a class-path convention for our category names allows one to pseudo-inherit for logging levels and appenders! The following example should help clarify this concept.

The overall premise is that when you request a logger with a category name LogBox will search for it's configuration. If LogBox does not find a configuration for the category name it will try to locate its closest ancestor for logging levels and appenders. If LogBox cannot find an ancestor the message will be logged using the root logger information. For example, let's say we define some appenders like this:

// Appenders
config.appender(
  name="console",
  class="logbox.system.logging.appenders.ConsoleAppender"
);
config.appender(
  name="file",
  class="logbox.system.logging.appenders.FileAppender",
  properties={ filePath="/logs" }
)

And some categories like this:

// Explicit Categories
config.category(
  name="coldbox.system",
  levelMin=config.logLevels.INFO,
  appenders="console"
);

// Implicit Categories
config.error(
  "coldbox.system.plugins"
);
// same as
config.cateogry(
  name="coldbox.system.plugins",
  levelMax="ERROR"
);

Then, let's say we request the following logger objects and logged some info:

logger = logBox.getLogger( "coldbox.system.plugins.BeanFactory" );
logger.info( "hello info" );
logger.error( "wow and error occurred" );

logger = logBox.getLogger( "coldbox.system.interceptors.SES" );
logger.info( "hello info" );
logger.debug( "a cool debug message" );

Information All example code snippets are using a getLogger( "categoryname" ) call instead of our preferred approach of getLogger( this ) because we want to showcase which category we are talking about. Please take this into consideration.

Category	Configured Levels	Assigned Levels	Appenders
root	FATAL-DEBUG	FATAL-DEBUG	console,file
coldbox.system	INFO-DEBUG	INFO-DEBUG	console
coldbox.system.plugins	ERROR	ERROR	*
coldbox.system.interceptors.SES	coldbox.system.interceptors.SES	INFO-DEBUG from coldbox.system	console from coldbox.system
coldbox.system.plugins.BeanFactory	NONE	ERROR from coldbox.system.plugins	*

Since we requested the category: coldbox.system.plugins.BeanFactory, LogBox tries to locate it, but it has not been defined, so it takes off the last item in the category name. Now it will search for a category of: coldbox.system.plugins via pseudo-inheritance. However, now coldbox.system.plugins has been found and it has been configured to only listen to error messages. Therefore, the coldbox.system.plugins.BeanFactory logger can ONLY log error messages according to it's inherited category. So the info() message will be ignored, and the error() message will be sent to both the FileAppender and the ConsoleAppender!

The second logger is called coldbox.system.interceptors.SES, LogBox tries to match a category but fails, so it now searches for a logger called coldbox.system.interceptors. It still cannot find it so it continues up the package chain and finds the coldbox.system logger which has been set with a minimum of INFO level and ONLY the console appender. So the messages that get logged is the logger.info() and the logger.debug() message and they will be sent to the console appender.

These examples should give you insight into category inheritance and the power they provide. You can easily turn toggle logging for entire packages with a single category definition. However, this is great only if you follow the dot notation conventions. Below is a sample generic chart sample:

Category	Configured Levels	Assigned Levels
root	FATAL-DEBUG	FATAL-DEBUG
x	NONE	FATAL-DEBUG from root
x.y	INFO	INFO
x.y.z	NONE	INFO from x.y