code: private File getStorageDir() {
          String externalStorageState = Environment.getExternalStorageState();
          if (!externalStorageState.equals(Environment.MEDIA_MOUNTED)) {
              return null;
          }
  
          // 默认在外置程序包下面.logs 文件夹
          File file = getExternalStorageDirectory();
  
          if (fileName.startsWith("/")) {
              File tmp = new File(fileName);
              if (tmp.isDirectory())
                  return tmp;
  
              return new File(file, getFileNameWithoutExtension(fileName));
          }
  
          String tmp = Environment.getExternalStorageDirectory().getPath();
          if (fileName.startsWith(tmp)) {
              file = new File(file, fileName.replace(tmp, ""));
              return file;
          }
  
          file = new File(file, "logs");
          file.mkdirs();
          return file;
      }
docs: 非wrap 的情况下, 如果不是以 /mnt/sdcard/, mnt/sdcard/ 开头的直接定位到此
  
  @return