code: public static byte[] getKey(Integer length) {
          if (!AESUtil.SHORT.equals(length) && !AESUtil.MIDDLE.equals(length) && !AESUtil.LONG.equals(length)) {
              throw new RuntimeException("指定的KeySize不正确");
          }
          SecretKey key = null;
          try {
              KeyGenerator keyGen = KeyGenerator.getInstance("AES");
              keyGen.init(length);
              key = keyGen.generateKey();
          } catch (NoSuchAlgorithmException e) {
              throw new RuntimeException(e);
          }
          return key.getEncoded();
      }
docs: 获取指定keysize的AES密钥,通过AESUtils类的静态常量指定
  
  @return 返回密钥的字节数组, 失败返回null