[[Logging_Loggers]]
= Loggers

ifdef::env-github[]
:tip-caption: :bulb:
:note-caption: :information_source:
:important-caption: :heavy_exclamation_mark:
:caution-caption: :fire:
:warning-caption: :warning:
endif::[]

[IMPORTANT]
This is still a work in progress. Please feel free to edit any mistakes
you find icon:smile-o[role="yellow"]


== Overview

Loggers are used to log messages. A logger is defined by a category
generally consisting of a package name or a class name.

A logger is the first step to determining if a messages should be logged
or not. If a logger is defined with a level, the level of the message
must be greater than the level defined on the logger. The filter is then
checked next and the rules of the filter will determine whether or not
the messages is said to be loggable.

[[logger-resource]]
=== Logger Resource

A logger resource uses the path `subsystem=logging/logger=$category`
where `$category` is the of the logger. For example to a logger named
org.wildfly.example would have a resource path of
`subsystem=logging/logger=org.wildfly.example`.

A logger as 4 writeable attributes;

* <<filter-spec,filter-spec>>
* <<level,#handlers>>
* <<level,#level>>
* link:#Loggers-use-parent-handlers[use-parent-handlers]

[IMPORTANT]

You may notice that the `category` and `filter` attributes are missing.
While `filter` is writable it may be deprecated and removed in the
future. Both attributes are still on the resource for legacy reasons.

==== filter-spec

The `filter-spec` attribute is an expression based string to define
filters for the logger.

[IMPORTANT]

Filters on loggers are not inherited.

==== handlers

The `handlers` attribute is a list of handler names that should be
attached to the logger. If the
<<use-parent-handlers,use-parent-handlers>>
attribute is set to `true` and the log messages is determined to be
loggable, parent loggers will continue to be processed.

==== level

The `level` attribute allows the minimum level to allow messages to be
logged at for the logger.

[[use-parent-handlers]]
==== use-parent-handlers

The `use-parent-handlers` attribute is a boolean attribute to determine
whether or not parent loggers should also process the log message.

[[root-logger-resource]]
=== Root Logger Resource

The `root-logger` is similar to a
<<logger-resource,#Logger Resource>> only it has no
category and it's name is must be `ROOT`.

[[logger-hierarchy]]
=== Logger Hierarchy

A logger hierarchy is defined by it's category. The category is a `.`
(dot) delimited string generally consisting of the package name or a
class name. For example the logger `org.wildfly` is the parent logger of
`org.wildfly.example`.
