code: public static byte[] generateAesKey(int keysize) {
  		try {
  			KeyGenerator keyGenerator = KeyGenerator.getInstance(AES_ALG);
  			keyGenerator.init(keysize);
  			SecretKey secretKey = keyGenerator.generateKey();
  			return secretKey.getEncoded();
  		} catch (GeneralSecurityException e) {
  			throw ExceptionUtil.unchecked(e);
  		}
  	}
docs: 生成AES密钥,可选长度为128,192,256位.