Support log4j2 with yaml format

[anibalgomezprojects]

Log4j2 is supporting log4j2.yml and yaml and spring boot log4j2 is not, any solution?

https://issues.apache.org/jira/browse/LOG4J2-427

Regards!

Automatic Configuration
Log4j has the ability to automatically configure itself during initialization. When Log4j starts it will locate all the ConfigurationFactory plugins and arrange then in weighted order from highest to lowest. As delivered, Log4j contains three ConfigurationFactory implementations: one for JSON, one for YAML, and one for XML.

Log4j will inspect the "log4j.configurationFile" system property and, if set, will attempt to load the configuration using the ConfigurationFactory that matches the file extension.
If no system property is set the YAML ConfigurationFactory will look for log4j2-test.yaml or log4j2-test.yml in the classpath.
If no such file is found the JSON ConfigurationFactory will look for log4j2-test.json or log4j2-test.jsn in the classpath.
If no such file is found the XML ConfigurationFactory will look for log4j2-test.xml in the classpath.
If a test file cannot be located the YAML ConfigurationFactory will look for log4j2.yaml or log4j2.yml on the classpath.
If a YAML file cannot be located the JSON ConfigurationFactory will look for log4j2.json or log4j2.jsn on the classpath.
If a JSON file cannot be located the XML ConfigurationFactory will try to locate log4j2.xml on the classpath.
If no configuration file could be located the DefaultConfiguration will be used. This will cause logging output to go to the console.

[wilkinsona]

Log4J 2's YAML processing uses Jackson's YAML support, whereas Spring Boot uses SnakeYAML. It's easy to fix this if we're happy to require a jackson-dataformat-yaml dependency. It's harder, but still possible, if we want to allow SnakeYAML to be used - we'd have to write our own ConfigurationFactory for YAML that uses SnakeYAML.

@philwebb Do you have a preference?

[philwebb]

I don't think we should write our own. Perhaps optional jackson-dataformat-yaml support?

[philwebb]

We should push this back to 1.3 if it's risky or complicated.

[cemo]

Latest Jackson improvements is awesome and definitely +1 for jackson-dataformat-yaml. FWIW Jackson is also using SnakeYAML and shading it.