Matt Sicker created LOG4J2-2803:
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Summary: Create standardized scopes and dependency injection API
Key: LOG4J2-2803
URL: https://issues.apache.org/jira/browse/LOG4J2-2803
Project: Log4j 2
Issue Type: Epic
Components: Configuration, Core, Plugins
Reporter: Matt Sicker
Assignee: Matt Sicker
Fix For: 3.0.0
In Log4j 2.x, the plugin API provides several {{@Plugin}} annotations which are
used for performing dependency injection of configuration-scoped data (plugin
attributes, values) and other configuration-scoped plugins (plugin elements).
While this API works well enough for a large majority of our use cases, the
remaining injection points include the {{Node}} and {{Configuration}}
corresponding to the currently parsed node and configuration respectively which
are used to perform manual lookups and other glue code that would be more
appropriately modeled through inversion of control with a more complete
dependency injection API.
In Log4j 3.0, this epic introduces a new plugin system API inspired by
[CDI|https://docs.jboss.org/cdi/api/2.0/],
[@Inject|https://docs.oracle.com/javaee/6/api/javax/inject/Inject.html], and
[Guice|https://github.com/google/guice] that maintains full backward
compatibility with the annotations from 2.x so that plugins do not need to be
needlessly rewritten for 3.x. This epic was initially developed as a result of
work done in LOG4J2-2694.
Beyond the dependency injection API itself, this epic is motivated by the
following goals:
* Simplify plugin classes that currently require manual method calls to
{{Configuration}} or {{Node}}.
* Unify the various ad hoc dependency injection for configuration-scoped or
singleton-scoped classes (the latter which are overridden via system
properties) including:
** {{StrSubstitutor}}
** {{ConfigurationScheduler}} (or scheduled tasks in general)
** {{ScriptManager}}
** {{WatchManager}}
** {{NanoClock}}
** {{ShutdownCallbackRegistry}}
** {{Clock}}
** {{ContextSelector}}
** {{ConfigurationFactory}}{{}}
** {{LogEventFactory}}
** {{ContextDataFactory}}
* Make dependencies between classes more explicit via inversion of control
which allows for easier testing and modularity.
* Avoid the use of manual configuration handling at the API level of any
plugins including basic string parsing (as currently supported through the
{{TypeConverter}} API), class loading from strings, and ad hoc reflection. This
relates to the changes made in LOG4J2-2621 and LOG4J2-1917.
* Provide smart initialization logic to continue (or maintain) improvements to
startup time and avoid loading plugins that aren't referenced in the loaded
configuration.
* Provide scopes for other ad hoc scopes/contexts used in various plugins such
as HTTP request, HTTP session, servlet context, etc.
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