Extending Log4j 2 Configuration

Custom Configurations

Log4j 2 provides a few ways for applications to create their own custom configurations.

Add a New Configuration via ConfigurationFactory

The easiest way to create a custom Configuration is to extend one of the standard Configuration classes (XMLConfiguration, JSONConfiguration) and then create a new ConfigurationFactory for the extended class. After the standard configuration completes the custom configuration can be added to it.

The example below shows how to extend XMLConfiguration to manually add an Appender and a LoggerConfig to the configuration.

@Plugin(name = "MyXMLConfigurationFactory", category = "ConfigurationFactory")
@Order(10)
public class MyXMLConfigurationFactory extends ConfigurationFactory {

    /**
     * Valid file extensions for XML files.
     */
    public static final String[] SUFFIXES = new String[] {".xml", "*"};

    /**
     * Return the Configuration.
     * @param source The InputSource.
     * @return The Configuration.
     */
    public Configuration getConfiguration(InputSource source) {
        return new MyXMLConfiguration(source, configFile);
    }

    /**
     * Returns the file suffixes for XML files.
     * @return An array of File extensions.
     */
    public String[] getSupportedTypes() {
        return SUFFIXES;
    }
}

public class MyXMLConfiguration extends XMLConfiguration {
    public MyXMLConfiguration(final ConfigurationFactory.ConfigurationSource configSource) {
      super(configSource);
    }

    @Override
    protected void doConfigure() {
        super.doConfigure();
        final LoggerContext ctx = (LoggerContext) LogManager.getContext(false);
        final Layout layout = PatternLayout.createLayout(PatternLayout.SIMPLE_CONVERSION_PATTERN, config, null,
              null,null, null);
        final Appender appender = FileAppender.createAppender("target/test.log", "false", "false", "File", "true",
              "false", "false", "4000", layout, null, "false", null, config);
        appender.start();
        addAppender(appender);
        LoggerConfig loggerConfig = LoggerConfig.createLogger("false", "info", "org.apache.logging.log4j",
              "true", refs, null, config, null );
        loggerConfig.addAppender(appender, null, null);
        addLogger("org.apache.logging.log4j", loggerConfig);
    }
}

Programattically Adding to the Current Configuration

Applications sometimes have the need to customize logging separate from the actual configuration. Log4j allows this although it suffers from a few limitations:

If the configuration file is changed the configuration will be reloaded and the manual changes will be lost.
Modification to the running configuration requires that all the methods being called (addAppender and addLogger) be synchronized.

As such, the recommended approach for customizing a configuration is to extend one of the standard Configuration classes, override the setup method to first do super.setup() and then add the custom Appenders, Filters and LoggerConfigs to the configuration before it is registered for use.

The following example adds an Appender and a new LoggerConfig using that Appender to the current configuration.

        final LoggerContext ctx = (LoggerContext) LogManager.getContext(false);
        final Configuration config = ctx.getConfiguration();
        Layout layout = PatternLayout.createLayout(PatternLayout.SIMPLE_CONVERSION_PATTERN, config, null,
            null,null, null);
        Appender appender = FileAppender.createAppender("target/test.log", "false", "false", "File", "true",
            "false", "false", "4000", layout, null, "false", null, config);
        appender.start();
        config.addAppender(appender);
        AppenderRef ref = AppenderRef.createAppenderRef("File", null, null);
        AppenderRef[] refs = new AppenderRef[] {ref};
        LoggerConfig loggerConfig = LoggerConfig.createLogger("false", "info", "org.apache.logging.log4j",
            "true", refs, null, config, null );
        loggerConfig.addAppender(appender, null, null);
        config.addLogger("org.apache.logging.log4j", loggerConfig);
        ctx.updateLoggers();
}