docs: public static void init() {
          String tracerClassName = System.getProperty(OPENTRACING_TRACER_CLASS_NAME);
          Preconditions.checkNotNull(tracerClassName, "Can not find opentracing tracer implementation class via system property `%s`", OPENTRACING_TRACER_CLASS_NAME);
          try {
              init((Tracer) Class.forName(tracerClassName).newInstance());
          } catch (final ReflectiveOperationException ex) {
              throw new ShardingException("Initialize opentracing tracer class failure.", ex);
          }
      }