code: public static <T> OperatorLogging<T> log(String onNextFormat) {
          return Logging.<T> logger().onNextFormat(onNextFormat).log();
      }
docs: Returns an {@link Operator} that logs every <i>onNext</i> value using a
  {@link Logger} based on the current class. Is equivalent to
  <tt>logger().showValue().log()</tt>.
  
  @return operator that logs every <i>onNext</i> value.