code: public static FilePool getOrCreatePool(String path, long limit) {
          FilePool pool = pools.get(path);
          if (pool == null) {
              pool = new NutFilePool(path, limit);
              pool = new SynchronizedFilePool(pool);
              pools.put(path, pool);
          }
          return pool;
      }
docs: 获取指定路径下的FilePool,如果没有就新建一个
  @param path 临时文件夹
  @param limit 最大文件数量
  @return 已有或新建的FilePool同步实例