Does Log4j2 support file inclusion mechanism like Logback does ? This is for including parts of a configuration file from another file (containing appenders, loggers etc.)
As an FYI - Here is how it works in Logback:
Joran supports including parts of a configuration file from another file. This is done by declaring a element, as shown below:
Example: File include (logback-examples/src/main/java/chapters/configuration/containingConfig.xml)
<configuration>
<include file="src/main/java/chapters/configuration/includedConfig.xml"/>
<root level="DEBUG">
<appender-ref ref="includedConsole" />
</root>
The target file MUST have its elements nested inside an element. For example, a ConsoleAppender could be declared as:
Example: File include (logback-examples/src/main/java/chapters/configuration/includedConfig.xml)
<included>
<appender name="includedConsole" class="ch.qos.logback.core.ConsoleAppender">
<encoder>
<pattern>"%d - %m%n"</pattern>
</encoder>
</appender>
</included>
XInclude can be used, but isn't an ideal solution. When using XInclude the include files themselves have to define a single top level element such as Appenders/Loggers/Properties.
Here's an example of how you could use it:
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="error" xmlns:xi="http://www.w3.org/2001/XInclude">
<!-- this will override the log pattern defined in the included log4j-properties.xml -->
<Properties>
<Property name="log-pattern">jit %d %-5p [%t] %C{1.} - %m%n</Property>
</Properties>
<xi:include href="log4j2-properties.xml" />
<xi:include href="log4j2-appenders.xml" />
<xi:include href="log4j2-loggers.xml" />
</Configuration>
As an example include the log4j2-properties.xml could look like:
<?xml version="1.0" encoding="UTF-8"?>
<Properties>
<!-- define the log pattern as a property so that it can be overridden -->
<Property name="log-pattern">%d %-5p [%t] %C{1.} - %m%n</Property>
</Properties>
You can make XIncludes optional by using an empty "fallback" block. However in the latest version of log4j2 that is available this results in a warning message coming out of Xerces (since the DefaultErrorHandler is being used by log4j2).
<xi:include href="log4j2-optional.xml">
<xi:fallback />
</xi:include>
A slightly different but similar mechanism exists in Log4j2, it supports XInclude.
See https://issues.apache.org/jira/browse/LOG4J2-341 for details. (This needs to be documented better...)
