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Apache Log4j 2 is an upgrade to Log4j that provides significant improvements over its predecessor, Log4j 1.x, and provides many of the improvements available in Logback while fixing some inherent problems in Logback’s architecture.

自动配置

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

  1. Log4j will inspect the “log4j2.configurationFile” system property and, if set, will attempt to load the configuration using the ConfigurationFactory that matches the file extension. Note that this is not restricted to a location on the local file system and may contain a URL.
  2. If no system property is set the properties ConfigurationFactory will look for log4j2-test.properties in the classpath.
  3. If no such file is found the YAML ConfigurationFactory will look for log4j2-test.yaml or log4j2-test.yml in the classpath.
  4. If no such file is found the JSON ConfigurationFactory will look for log4j2-test.json or log4j2-test.jsn in the classpath.
  5. If no such file is found the XML ConfigurationFactory will look for log4j2-test.xml in the classpath.
  6. If a test file cannot be located the properties ConfigurationFactory will look for log4j2.properties on the classpath.
  7. If a properties file cannot be located the YAML ConfigurationFactory will look for log4j2.yaml or log4j2.yml on the classpath.
  8. If a YAML file cannot be located the JSON ConfigurationFactory will look for log4j2.json or log4j2.jsn on the classpath.
  9. If a JSON file cannot be located the XML ConfigurationFactory will try to locate log4j2.xml on the classpath.
  10. If no configuration file could be located the DefaultConfiguration will be used. This will cause logging output to go to the console.

reference:
Automatic Configuration