code: public static byte[] initKey() throws Exception{
  		//密钥生成器
  		KeyGenerator keyGen = KeyGenerator.getInstance("AES");
  		//初始化密钥生成器
  		keyGen.init(128);  //默认128，获得无政策权限后可用192或256
  		//生成密钥
  		SecretKey secretKey = keyGen.generateKey();
  		return secretKey.getEncoded();
  	}
docs: 生成密钥
  @throws Exception