Question

我使用this docker图片来安装Mosquitto MQTT。现在它正在运行并在终端中显示以下消息：

1515680808: mosquitto version 1.4.14 (build date Mon, 10 Jul 2017 23:48:43 +0100) starting
1515680808: Config loaded from /mqtt/config/mosquitto.conf.
1515680808: Opening websockets listen socket on port 9001.
1515680808: Opening ipv4 listen socket on port 1883.
1515680808: Opening ipv6 listen socket on port 1883.

然后我创建了一个简单的Maven项目：

<dependency>
    <groupId>org.apache.spark</groupId>
    <artifactId>spark-streaming-mqtt_2.11</artifactId>
    <version>1.6.3</version>
</dependency>

我尝试使用下面显示的代码将一些数据发布到主题。我指向localhost:1883作为MqttBrokerUrl和主题test。但是，我收到了这个错误：

线程“main”中的异常java.lang.NullPointerException at org.eclipse.paho.client.mqttv3.MqttConnectOptions.validateURI（MqttConnectOptions.java:457）在 org.eclipse.paho.client.mqttv3.MqttAsyncClient。（MqttAsyncClient.java:273）在 org.eclipse.paho.client.mqttv3.MqttAsyncClient。（MqttAsyncClient.java:167）在 org.eclipse.paho.client.mqttv3.MqttClient。（MqttClient.java:224）在org.test.MQTTPublisher $ .main（MQTTPublisher.scala：37）at org.test.MQTTPublisher.main（MQTTPublisher.scala）

代码：

package org.test

import org.apache.log4j.{Level, Logger}
import org.eclipse.paho.client.mqttv3._
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence
import org.apache.spark.storage.StorageLevel
import org.apache.spark.streaming.{Seconds, StreamingContext}
import org.apache.spark.streaming.mqtt._
import org.apache.spark.SparkConf

object MQTTPublisher {

  def main(args: Array[String]) {
    if (args.length < 2) {
      System.err.println("Usage: MQTTPublisher <MqttBrokerUrl> <topic>")
      System.exit(1)
    }

    // Set logging level if log4j not configured (override by adding log4j.properties to classpath)
    if (!Logger.getRootLogger.getAllAppenders.hasMoreElements) {
      Logger.getRootLogger.setLevel(Level.WARN)
    }

    val Seq(brokerUrl, topic) = args.toSeq

    var client: MqttClient = null

    try {
      val persistence = new MemoryPersistence()
      client = new MqttClient("localhost:1883", MqttClient.generateClientId(), persistence)

      client.connect()

      val msgtopic = client.getTopic(topic)
      val msgContent = "test test test"
      val message = new MqttMessage(msgContent.getBytes("utf-8"))

      while (true) {
        try {
          msgtopic.publish(message)
          println(s"Published data. topic: ${msgtopic.getName()}; Message: $message")
        } catch {
          case e: MqttException if e.getReasonCode == MqttException.REASON_CODE_MAX_INFLIGHT =>
            Thread.sleep(10)
            println("Queue is full, wait for to consume data from the message queue")
        }
      }
    } catch {
      case e: MqttException => println("Exception Caught: " + e)
    } finally {
      if (client != null) {
        client.disconnect()
      }
    }
  }
}

Answer 1

MqttClient()构造函数采用URI。

你提供的只是一个主机名和端口号（localhost:1883），它缺少一个应该是tcp://的协议部分（这是库所期望的并且获得null这真的应该抛出一个更好的错误。）

您需要将行更改为

client = new MqttClient("tcp://localhost:1883", MqttClient.generateClientId(), persistence);

Answer 2

我认为你提供了错误的Url，即你没有指定它必须连接的协议，这是我的预感。

尝试将网址更改为：

tcp://localhost:1883

我认为它会起作用！休息对我来说似乎很好。

有关工作示例，请参阅：https://github.com/shiv4nsh/scala-mqtt-client-rasberrypi-starter-kit/blob/master/src/main/scala/com/knoldus/MQTTPublisher.scala

如何使用MQTT发布数据

2 个答案: