import io.netty.handler.codec.mqtt.MqttConnAckVariableHeader; //导入依赖的package包/类
public static MqttConnAckMessage connack(MqttConnectReturnCode returnCode, boolean sessionPresent) {
	MqttFixedHeader fixedHeader = new MqttFixedHeader(MqttMessageType.CONNACK, false, MqttQoS.AT_MOST_ONCE, false,
			2);
	MqttConnAckVariableHeader variableHeader = new MqttConnAckVariableHeader(returnCode, sessionPresent);

	return new MqttConnAckMessage(fixedHeader, variableHeader);
}
 

import io.netty.handler.codec.mqtt.MqttConnAckVariableHeader; //导入依赖的package包/类
private MqttConnAckMessage createMqttConnAckMsg(MqttConnectReturnCode returnCode) {
  MqttFixedHeader mqttFixedHeader = new MqttFixedHeader(CONNACK, false, AT_MOST_ONCE, false, 0);
  MqttConnAckVariableHeader mqttConnAckVariableHeader = new MqttConnAckVariableHeader(returnCode, true);
  return new MqttConnAckMessage(mqttFixedHeader, mqttConnAckVariableHeader);
}
 

import io.netty.handler.codec.mqtt.MqttConnAckVariableHeader; //导入依赖的package包/类
private static MqttConnAckMessage createConnAckMessage(MqttConnectReturnCode code) {
    MqttFixedHeader mqttFixedHeader =
            new MqttFixedHeader(MqttMessageType.CONNACK, false, MqttQoS.AT_MOST_ONCE, false, 2);
    MqttConnAckVariableHeader mqttConnAckVariableHeader = new MqttConnAckVariableHeader(code, true);
    return new MqttConnAckMessage(mqttFixedHeader, mqttConnAckVariableHeader);
}
 

import io.netty.handler.codec.mqtt.MqttConnAckVariableHeader; //导入依赖的package包/类
void sendConnack(MqttConnectReturnCode returnCode) {
   MqttFixedHeader fixedHeader = new MqttFixedHeader(MqttMessageType.CONNACK, false, MqttQoS.AT_MOST_ONCE, false, 0);
   MqttConnAckVariableHeader varHeader = new MqttConnAckVariableHeader(returnCode, true);
   MqttConnAckMessage message = new MqttConnAckMessage(fixedHeader, varHeader);
   sendToClient(message);
}