docs: public HDFSDistributor setFileRoot(String fileRoot) {
          this.hdfsFileRoot = fileRoot;
          this.mapperInputFilePath = new Path(hdfsFileRoot + "/input.dat");
          if (mapperOutputFileName != null) {
              this.mapperOutputFilePath = new Path(hdfsFileRoot + "/" + mapperOutputFileName);
          }
          return this;
      }