docs: @Override
      public void set(String key, byte[] data) {
          File f = new File(directory, hash(key));
          FileOutputStream fo = null;
          try {
              fo = new FileOutputStream(f);
              fo.write(data);
          } catch (IOException e) {
              e.printStackTrace();
          }
          if (fo != null) {
              try {
                  fo.close();
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
      }