code: public static Checksum checksum(InputStream in, Checksum checksum) throws IORuntimeException {
  		Assert.notNull(in, "InputStream is null !");
  		if (null == checksum) {
  			checksum = new CRC32();
  		}
  		try {
  			in = new CheckedInputStream(in, checksum);
  			IoUtil.copy(in, new NullOutputStream());
  		} finally {
  			IoUtil.close(in);
  		}
  		return checksum;
  	}
docs: 计算流的校验码，计算后关闭流
  
  @param in 流
  @param checksum {@link Checksum}
  @return Checksum
  @throws IORuntimeException IO异常
  @since 4.0.10