public static String initializeLogging() throws IOException {
        System.setProperty("org.slf4j.simpleLogger.logFile", "System.out");
        System.setProperty("org.slf4j.simpleLogger.showDateTime", "true");
        System.setProperty("org.slf4j.simpleLogger.dateTimeFormat", "yyyyMMdd.HH:mm:ss.SSS");
        // Peek at mdw.yaml to find default logging level, but do not initialize PropertyManager
        // which could initialize slf4j prematurely.  (Works only with yaml config file).
        String mdwLogLevel = null;
        File mdwYaml = getConfigurationFile("mdw.yaml");
        if (mdwYaml.exists()) {
            YamlProperties yamlProps = new YamlProperties("mdw", mdwYaml);
            mdwLogLevel = yamlProps.getString("mdw.logging.level");
            if (mdwLogLevel != null) {
                if (mdwLogLevel.equals("MDW_DEBUG"))
                    mdwLogLevel = "TRACE";
                System.setProperty("org.slf4j.simpleLogger.log.com.centurylink.mdw", mdwLogLevel.toLowerCase());
            }
        }
        return mdwLogLevel;
    }
public static String initializeLogging ( ) throws IOException { System . setProperty ( "org.slf4j.simpleLogger.logFile" , "System.out" ) ; System . setProperty ( "org.slf4j.simpleLogger.showDateTime" , "true" ) ; System . setProperty ( "org.slf4j.simpleLogger.dateTimeFormat" , "yyyyMMdd.HH:mm:ss.SSS" ) ; String mdwLogLevel = null ; File mdwYaml = getConfigurationFile ( "mdw.yaml" ) ; if ( mdwYaml . exists ( ) ) { YamlProperties yamlProps = new YamlProperties ( "mdw" , mdwYaml ) ; mdwLogLevel = yamlProps . getString ( "mdw.logging.level" ) ; if ( mdwLogLevel != null ) { if ( mdwLogLevel . equals ( "MDW_DEBUG" ) ) mdwLogLevel = "TRACE" ; System . setProperty ( "org.slf4j.simpleLogger.log.com.centurylink.mdw" , mdwLogLevel . toLowerCase ( ) ) ; } } return mdwLogLevel ; }
For Spring Boot with slf4j SimpleLogger, an opportunity to initialize logging before Spring starts logging.
Otherwise for slf4j, properties have already been defaulted before we have a chance to set them.

See mdw-spring-boot AutoConfig for initialization of logback for pure Spring Boot apps.