std::string getMacAddress(JNIEnv* env) {
  //通过JNI找到java中的NetworkInterface类
  jclass cls_networkInterface = env->FindClass("java/net/NetworkInterface");
  if (cls_networkInterface == 0) {
    return "";
  }
  //找到getByName方法
  jmethodID jmethodID_getByName =
      env->GetStaticMethodID(cls_networkInterface, "getByName",
                             "(Ljava/lang/String;)Ljava/net/NetworkInterface;");
  if (jmethodID_getByName == 0) {
    return "";
  }

  jstring wlan = env->NewStringUTF("wlan0");

  //调用getByname方法返回NetworkInterface的实例
  jobject jobject_networkInterface = env->CallStaticObjectMethod(
      cls_networkInterface, jmethodID_getByName, wlan);

  //找到getHardAddress方法
  jmethodID jmethodID_getHardwareAddress =
      env->GetMethodID(cls_networkInterface, "getHardwareAddress", "()[B");
  if (jmethodID_getHardwareAddress == 0) {
    return "";
  }

  //调用getHardAddress方法获取MAC地址的byte[]数组
  jbyteArray jbyte_mac = (jbyteArray)env->CallObjectMethod(
      jobject_networkInterface, jmethodID_getHardwareAddress);
  jsize oldsize = env->GetArrayLength(jbyte_mac);
  int len = (int)oldsize;

  char* data = (char*)env->GetByteArrayElements(jbyte_mac, 0);
  std::string MacAddress;
  MacAddress.reserve(len * 2);
  char buffer[3] = {0};
  for (int i = 0; i < len; i++) {
    snprintf(buffer, sizeof(buffer), "%02X", data[i]);
    MacAddress.append(buffer);
  }
  return MacAddress;
}