code: public static Single<Boolean> exists(String path) {
          return SingleRxXian.call("cosService", "cosCheckFileExists", new JSONObject() {{
              put("path", path);
          }}).map(UnitResponse::dataToBoolean);
      }
docs: check whether the cos file exists
  
  @param path the cos path
  @return true if exits, false if not exits, error on exception.