MqttException（0）-AndroidThings上的java.net.NoRouteToHostException

我正在试用Android系统，它仍处于预览模式。
通过代码与wifi和本地网络通信面临许多挑战
其中一个例子是在RPi3上制作Android作为MQTT代理。
我不确定问题是出在MQTT代码上还是出在Android上。

有人能帮我确定这个问题吗？
这是我的代码：

package com.example.androidthings.myproject;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;

import com.google.android.things.pio.Gpio;
import com.google.android.things.pio.PeripheralManagerService;

import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken;
import org.eclipse.paho.client.mqttv3.MqttCallback;
import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.eclipse.paho.client.mqttv3.MqttMessage;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;

import java.io.IOException;

    public class MainActivity extends Activity implements MqttCallback{
    private static final String TAG = MainActivity.class.getSimpleName();

    public static final String MOTOR_A_PIN_1 = "BCM21"; //physical pin #40
    public static final String MOTOR_A_PIN_2 = "BCM20"; //physical pin #38
    public static final String MOTOR_B_PIN_1 = "BCM24"; //physical pin #18
    public static final String MOTOR_B_PIN_2 = "BCM23"; //physical pin #16

    private Gpio motorAPin1;
    private Gpio motorAPin2;
    private Gpio motorBPin1;
    private Gpio motorBPin2;

    private MqttClient client;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d(TAG, "onCreate.....Motor MQTT");

        try {
            MemoryPersistence persistance = new MemoryPersistence();
            client = new MqttClient("tcp://127.0.0.1:1883", "AndroidThingBroker", persistance);
            client.connect();

            String topic = "topic/androidthings";
            int qos = 1;
            client.subscribe(topic, qos);

        } catch (MqttException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }

        PeripheralManagerService service = new PeripheralManagerService();
        try {

            // Create GPIO connection for L293D (Motor will run through L293D).
            motorAPin1 = service.openGpio(MOTOR_A_PIN_1);
            // Configure as an output.
            motorAPin1.setDirection(Gpio.DIRECTION_OUT_INITIALLY_LOW);

            // Create GPIO connection for L293D (Motor will run through L293D).
            motorAPin2 = service.openGpio(MOTOR_A_PIN_2);
            // Configure as an output.
            motorAPin2.setDirection(Gpio.DIRECTION_OUT_INITIALLY_LOW);

            // Create GPIO connection for L293D (Motor will run through L293D).
            motorBPin1 = service.openGpio(MOTOR_B_PIN_1);
            // Configure as an output.
            motorBPin1.setDirection(Gpio.DIRECTION_OUT_INITIALLY_LOW);

            // Create GPIO connection for L293D (Motor will run through L293D).
            motorBPin2 = service.openGpio(MOTOR_B_PIN_2);
            // Configure as an output.
            motorBPin2.setDirection(Gpio.DIRECTION_OUT_INITIALLY_LOW);

        } catch (IOException e) {
            Log.e(TAG, "Error on PeripheralIO API", e);
        }


    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.d(TAG, "onDestroy");

        if (motorAPin1 != null) {
            try {
                motorAPin1.close();
            } catch (IOException e) {
                Log.e(TAG, "Error on PeripheralIO API", e);
            }
        }

        if (motorAPin2 != null) {
            try {
                motorAPin2.close();
            } catch (IOException e) {
                Log.e(TAG, "Error on PeripheralIO API", e);
            }
        }

        if (motorBPin1 != null) {
            try {
                motorBPin1.close();
            } catch (IOException e) {
                Log.e(TAG, "Error on PeripheralIO API", e);
            }
        }

        if (motorBPin2 != null) {
            try {
                motorBPin2.close();
            } catch (IOException e) {
                Log.e(TAG, "Error on PeripheralIO API", e);
            }
        }
    }

    @Override
    public void connectionLost(Throwable cause) {
        Log.d(TAG, "connectionLost....");
    }

    @Override
    public void messageArrived(String topic, MqttMessage message) throws Exception {
        String payload = new String(message.getPayload());
        Log.d(TAG, payload);
        // do stuff
    }

    @Override
    public void deliveryComplete(IMqttDeliveryToken token) {
        Log.d(TAG, "deliveryComplete....");
    }
}

错误：

12-27 15:03:58.898 2245-2245/com.example.androidthings.myproject W/System.err: 
Unable to connect to server (32103) - java.net.ConnectException: Connection refused
12-27 15:03:58.898 2245-2245/com.example.androidthings.myproject W/System.err:     at org.eclipse.paho.client.mqttv3.internal.TCPNetworkModule.start(TCPNetworkModule.java:79)
12-27 15:03:58.899 2245-2245/com.example.androidthings.myproject W/System.err:     at org.eclipse.paho.client.mqttv3.internal.ClientComms$ConnectBG.run(ClientComms.java:590)
12-27 15:03:58.899 2245-2245/com.example.androidthings.myproject W/System.err:     at java.lang.Thread.run(Thread.java:761)
12-27 15:03:58.899 2245-2245/com.example.androidthings.myproject W/System.err: Caused by: java.net.ConnectException: Connection refused
12-27 15:03:58.899 2245-2245/com.example.androidthings.myproject W/System.err:     at java.net.PlainSocketImpl.socketConnect(Native Method)
12-27 15:03:58.899 2245-2245/com.example.androidthings.myproject W/System.err:     at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:334)
12-27 15:03:58.899 2245-2245/com.example.androidthings.myproject W/System.err:     at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:196)
12-27 15:03:58.899 2245-2245/com.example.androidthings.myproject W/System.err:     at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:178)
12-27 15:03:58.899 2245-2245/com.example.androidthings.myproject W/System.err:     at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:356)
12-27 15:03:58.899 2245-2245/com.example.androidthings.myproject W/System.err:     at java.net.Socket.connect(Socket.java:586)
12-27 15:03:58.900 2245-2245/com.example.androidthings.myproject W/System.err:     at org.eclipse.paho.client.mqttv3.internal.TCPNetworkModule.start(TCPNetworkModule.java:70)
12-27 15:03:58.900 2245-2245/com.example.androidthings.myproject W/System.err:  ... 2 more

**编辑**
将ip地址更改为127.0.0.1，现在收到不同的错误堆栈。我已经更新了上面的错误日志

---

---

我的坏。。。MQTT代理已关闭。我想我可以在设备上创建一个代理。然后我意识到它应该在一台服务器上运行，而我在初始测试期间启动的那台服务器已经停机
当我使用Mosquitto启动代理服务器时，我现在可以从Android连接到它：D

如果

adb shell

那么

ping

正在工作，这意味着你的Android东西板有互联网连接，很可能不是你的问题

看看stacktrace

 client = new MqttClient("tcp://192.168.1.4:1883", "AndroidThingBroker", persistance);
 client.connect();

是抛出错误的代码，为了缩小问题范围，您可以在计算机上创建一个简单的Android应用程序，甚至只是一个java main方法，并找出路由问题是什么。也许ip是错误的，等等，但这似乎不是Android的问题（或者至少让你的代码作为java应用程序工作，以尽量减少可能性）

我还将删除此代码：

 catch (Exception e) {
        e.printStackTrace();
    }

---

这样你就不会捕获异常-你希望应用程序尽快中断，这样你就可以看到路由错误，而不是原始错误的副作用。

通过

adb shell

，尝试

ifconfig

或

ping

或其他方法，看看你的东西是如何连接到网络的。这是有效的。。我使用adb shell ifconfig获取发布者发送消息的ip地址。Java上同样的问题是防火墙问题。但我正在我的家庭网络上测试它。不确定根本原因是什么。ping正在处理8.8.8.8。我将IP地址更改为127.0.0.1，连接拒绝出现错误。