int i = 97;
 String bit = Integer.toBinaryString(i);
 //输出：97 对应的二进制数据为： 1100001
 System.out.println(i + "对应的二进制数据为： " + bit);

//byte 的取值范围：-128 到127
System.out.println(Byte.MIN_VALUE + "到" + Byte.MAX_VALUE);

 //1,得到cipher 对象（可翻译为密码器或密码系统）
 Cipher cipher = Cipher.getInstance("DES");
 //2，创建秘钥
 SecretKey key = KeyGenerator.getInstance("DES").generateKey();
 //3，设置操作模式（加密/解密）
 cipher.init(Cipher.ENCRYPT_MODE, key);
 //4，执行操作
 byte[] result = cipher.doFinal("黑马".getBytes());

//生成随机秘钥
SecretKey secretKey = KeyGenerator.getInstance("AES").generateKey();
//序列化秘钥到磁盘上
FileOutputStream fos = new FileOutputStream(new File("heima.key"));

ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(secretKey);

//从磁盘里读取秘钥
FileInputStream fis = new FileInputStream(new File("heima.key"));
ObjectInputStream ois = new ObjectInputStream(fis);
Key key = (Key) ois.readObject();

//创建密钥写法1
KeySpec keySpec = new DESKeySpec(key.getBytes());
SecretKey secretKey = SecretKeyFactory.getInstance(ALGORITHM).
generateSecret(keySpec);

//创建密钥写法2
//SecretKey secretKey = new SecretKeySpec(key.getBytes(), KEY_ALGORITHM);

Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM);
cipher.init(Cipher.DECRYPT_MODE, secretKey);
//得到key 后，后续代码就是Cipher 的写法，此处省略...

Cipher c = Cipher.getInstance("DES");

Cipher c = Cipher.getInstance("DES/CBC/PKCS5Padding");

//秘钥算法
private static final String KEY_ALGORITHM = "DES";
//加密算法：algorithm/mode/padding 算法/工作模式/填充模式
private static final String CIPHER_ALGORITHM = "DES/ECB/PKCS5Padding";
//秘钥
private static final String KEY = "12345678";//DES 秘钥长度必须是8 位或以上
//private static final String KEY = "1234567890123456";//AES 秘钥长度必须是16 位

//初始化秘钥
SecretKey secretKey = new SecretKeySpec(KEY.getBytes(), KEY_ALGORITHM);
Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM);

//加密
cipher.init(Cipher.ENCRYPT_MODE, secretKey);
byte[] result = cipher.doFinal(input.getBytes());

//AES、DES 在CBC 操作模式下需要iv 参数
IvParameterSpec iv = new IvParameterSpec(key.getBytes());

//加密
cipher.init(Cipher.ENCRYPT_MODE, secretKey, iv);