code: public static byte[] md5FileToByte(File file) {
          if (file == null) return null;
          FileInputStream   fis               = null;
          DigestInputStream digestInputStream = null;
          try {
              fis = new FileInputStream(file);
              MessageDigest md = MessageDigest.getInstance("MD5");
              digestInputStream = new DigestInputStream(fis, md);
              byte[] buffer = new byte[256 * 1024];
              while (digestInputStream.read(buffer) > 0) ;
              md = digestInputStream.getMessageDigest();
              return md.digest();
          } catch (NoSuchAlgorithmException | IOException e) {
              e.printStackTrace();
              return null;
          } finally {
              IOKit.closeQuietly(fis);
              IOKit.closeQuietly(digestInputStream);
          }
      }
docs: MD5加密文件
  
  @param file 文件
  @return 文件的MD5校验码