java md5

需求是，上传文件到ＨＤＦＳ，然后生成同名的ＭＤ５文件，基本示例如下：

public static String getMD5(InputStream inputStream)
    {
	    byte[] buffer = new byte[1024];
        int len = 0;
        try
        {
            MessageDigest messageDigest = MessageDigest.getInstance("MD5");
             while ((len = inputStream.read(buffer)) != -1)
            {
                messageDigest.update(buffer, 0, len);
            }
            BigInteger bigInteger = new BigInteger(1, messageDigest.digest());
            String hashtext = bigInteger.toString(16);
            while(hashtext.length() < 32 ){
            	  hashtext = "0"+hashtext;
            	}
            return hashtext;
        }
        catch (Exception e)
        {
            return null;
        }
    }
    

尤其需要注意的是第一段代码中的补０，如果不补０，这就会跟使用md5sum命令生成的数据有差别，这样使用md5sum -c 进行检查的时候，是会报错的。

报数据的格式不正确，提示错误不是校验失败。

	try {
				//mkdir -p then upload file
				String resDir = new File(softwareEntity.getResUri()).getParentFile().getPath();
				//System.out.println(resDir);
				HdfsUtil.getInstance().mkdir(resDir);
				HdfsUtil.getInstance().createFile(softwareEntity.getResUri(), file.getBytes());
				//upload the md5 file to the same directory
 	        String md5=EncryptionUtil.getMD5(file.getInputStream());
 	        StringBuilder sbFileCont = new StringBuilder(md5);
 			if(md5!=null)
 			{
 				String twoSpaces = "  " ;
 				sbFileCont.append(twoSpaces);
 				sbFileCont.append(file.getOriginalFilename());
 				sbFileCont.append("\n");
 				HdfsUtil.getInstance().createFile(softwareEntity.getResUri()+".md5",sbFileCont.toString().getBytes());
 			}
 			else
 				throw new ServiceException("Something wrong when gererate md5 digest for file" + softwareEntity.getResUri());

			} catch (IOException e) {
				throw new ServiceException("Save file error.", e);
			} catch (URISyntaxException e) {
				throw new ServiceException("upload file to hdfs error",e);
			}