code: protected void setupLogback() {
  
          // Check for Logback config file System Property
          // http://logback.qos.ch/manual/configuration.html
          //     -Dlogback.configurationFile=logback_prod.xml
          if (System.getProperty(LOGBACK_CONFIGURATION_FILE_PROPERTY) != null) {
              // Logback already configured
              return;
          }
  
          // Check for a logback configuration file declared in Fathom settings
          URL configFileUrl = settings.getFileUrl(LOGBACK_CONFIGURATION_FILE_PROPERTY, "classpath:conf/logback.xml");
  
          if (configFileUrl == null) {
              throw new FathomException("Failed to find Logback config file '{}'",
                      settings.getString(LOGBACK_CONFIGURATION_FILE_PROPERTY, "classpath:conf/logback.xml"));
          }
  
          LoggerContext context = (LoggerContext) LoggerFactory.getILoggerFactory();
  
          try (InputStream is = configFileUrl.openStream()) {
              JoranConfigurator configurator = new JoranConfigurator();
              configurator.setContext(context);
              context.reset();
              configurator.doConfigure(is);
              log.info("Configured Logback from '{}'", configFileUrl);
          } catch (IOException | JoranException je) {
              // StatusPrinter will handle this
          }
  
          StatusPrinter.printInCaseOfErrorsOrWarnings(context);
      }
docs: Setup Logback logging by optionally reloading the configuration file.