Java中的MessageDigest类加密详解

    public static MessageDigest getInstance(String algorithm)

  try
    {
        MessageDigest mdTemp1 = MessageDigest.getInstance("MD5");
        MessageDigest mdTemp2= MessageDigest.getInstance("MD5");
        MessageDigest mdTemp3= MessageDigest.getInstance("MD5");
        System.out.println("mdTemp1==mdTemp2?:"+(mdTemp1==mdTemp2));
        System.out.println("mdTemp2==mdTemp3?:"+(mdTemp2==mdTemp3));
    } catch (NoSuchAlgorithmException e)
    {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

MessageDigest.getInstance("SHA");
MessageDigest.getInstance("sha");
MessageDigest.getInstance("sHa");

public static void main(String[] args) throws NoSuchAlgorithmException {
		MessageDigest instance = MessageDigest.getInstance("md5");
		String UUID = java.util.UUID.randomUUID().toString();
		String pwd = "123456";
		String name = UUID+pwd;
		System.out.println("盐值："+UUID);
		System.out.println("密码："+pwd);
		System.out.println("盐值加密："+name);
		instance.update(name.getBytes());
		instance.reset();
		byte[] digest = instance.digest(name.getBytes());
		StringBuilder sb = new StringBuilder();
		for (byte b : digest) {
			String row = Integer.toHexString(b&0xff);
			if(row.length()==1){
				row = "0" + row;
			}
			sb.append(row);
		}
		System.out.println("加密后："+sb.toString());
	}

public void insertAttachement(String title, MultipartFile mFile) {
		if(title==null||title.trim().length()==0){
			throw new ServiceException("标题不能为空");
		}
		if(mFile==null){
			throw new ServiceException("不允许上传空文件");
		}
		byte[] bytes ;
		String digests= null;
		try {
            //将文件摘要转为字节
			bytes = mFile.getBytes();
            //将摘要后的字节数组进行MD5加密
			digests = DigestUtils.md5DigestAsHex(bytes);
		} catch (Exception e) {
			e.printStackTrace();
			throw new ServiceException("文件上传失败");
		}
		Integer rows = attachementsDao.getRowCountByDigest(digests);
		if(rows>0){
			throw new ServiceException("文件已上传，请勿重复上传！"); 
		}
		String fileName = mFile.getOriginalFilename();
		String contentType = mFile.getContentType();
		SimpleDateFormat sd = new SimpleDateFormat("yyyy-MM-dd");
		String timeDate = sd.format(new Date());
		String path = "F:"+File.separator+"upload"+File.separator+timeDate;
		File file = new File(path);
        //文件夹是否存在 不存在将创建
		if(!file.exists()){
			file.mkdirs();
		}
		File filepath = new File(path,fileName);
		try {
			mFile.transferTo(filepath);
		}  catch (IOException e) {
			e.printStackTrace();
			throw new ServiceException("文件上传失败");
		}
		Attachements att = new Attachements();
		att.setTitle(title);
		att.setFileName(fileName);
		att.setFilePath(filepath.getAbsolutePath());
		att.setFileDisgest(digests);
		att.setContentType(contentType);
		Integer row = attachementsDao.insertAttachement(att);
		if(row<1){
			throw new ServiceException("新增失败");
		}
	}