如何将 MQTT 的有效负载数据转换为 kafka 字符串类型

Question

现在我正试图从mqtt消息连接到kafka(实际上是kafka中的火花流)

我用过这个连接器https://github.com/evokly/kafka-connect-mqtt

和Spark-2.11.0，Kafka-0.1.1.1

类似的火花流输出

({"schema":{"type":"string","optional":false},"payload":"mqtt"},{"schema":{"type":"bytes","optional":false},"payload":"MTIzMTIz"})

和生产者代码

object mqttProducer {
def main(args: Array[String]) {
val brokerUrl = "tcp://ip"
val topic = "mqtt"
val msg = "123123"
var client: MqttClient = null
// Creating new persistence for mqtt client
val persistence = new MqttDefaultFilePersistence("/tmp")
try {
// mqtt client with specific url and client id
client = new MqttClient(brokerUrl, MqttClient.generateClientId, persistence)
client.connect()
val msgTopic = client.getTopic(topic)
val message = new MqttMessage(msg.getBytes("utf-8"))
while (true) {
msgTopic.publish(message)
println("Publishing Data, Topic : %s, Message : %s".format(msgTopic.getName, message))
Thread.sleep(1000)
}
}
catch {
case e: MqttException => println("Exception Caught: " + e)
}
finally {
client.disconnect()
}

和火花流kafka消费者代码

package hb.test1
import org.apache.kafka.common.serialization.StringDeserializer
import org.apache.spark.SparkConf
import org.apache.spark.streaming.Seconds
import org.apache.spark.streaming.StreamingContext
import org.apache.spark.streaming.kafka010.ConsumerStrategies.Subscribe
import org.apache.spark.streaming.kafka010.KafkaUtils
import org.apache.spark.streaming.kafka010.LocationStrategies.PreferConsistent
object test2 {
def main(args: Array[String]): Unit = {
val sparkConf = new SparkConf().setAppName("app")
val ssc = new StreamingContext(sparkConf, Seconds(1))    

val kafkaParams = Map[String, Object](
"bootstrap.servers" -> 
"servers ip",
"key.deserializer" -> classOf[StringDeserializer],
"value.deserializer" -> classOf[StringDeserializer],
"group.id" -> "use_a_separate_group_id_for_each_stream",
"auto.offset.reset" -> "latest",
"enable.auto.commit" -> (false: java.lang.Boolean)
)
val topics = Array("mqtt-kafka")
val stream = KafkaUtils.createDirectStream[String, String](
ssc,
PreferConsistent,
Subscribe[String, String](topics, kafkaParams)
)
val testStream = stream.map(x => (x.key, x.value))

testStream.print()
ssc.start()
ssc.awaitTermination()
}
}

我怎么能得到字符串而不是字节？请帮帮

Answer 1

有效载荷"MTIzMTIz"是以64为基础编码的字符串"123123"。如果您只想获取MQTT有效负载并将其发送到Kafka而不使用base64编码，则应该使用ByteArrayConverter。在同一mqtt连接器的配置中，我设置了如下值转换器：

"value.coverter"："io.confluent.connect.replicator.util.ByteArrayConverter">

上述ByteArrayConverter随Confluent Enterprise发行版提供，但也有其他开源的Kafka Connect ByteArrayCon转换器，如qubole/streamx Kafka-Connect-s3连接器中包含的转换器。

https://github.com/qubole/streamx/blob/8b9d43008d9901b8e6020404f137944ed97522e2/src/main/java/com/qubole/streamx/ByteArrayConverter.java

有KIP-128可以在Kafka Connect框架中添加一个标准的ByteArrayConverter

https://cwiki.apache.org/confluence/display/KAFKA/KIP-128%3A+添加+ByteArrayConverter+for+Kafka+Connect

更新：Kafka 0.11现已发布，并附带ByteArrayConverter。配置"value.converter": "org.apache.kafka.connect.converters.ByteArrayConverter"，您应该获得不带Base64编码的原始mqtt负载。