Flink 自定义source和sink，获取kafka的key，输出指定key

--------20190905更新-------　　

沙雕了，可以用  JSONKeyValueDeserializationSchema，接收ObjectNode的数据，如果有key，会放在ObjectNode中

if (record.key() != null) {
            node.set("key", mapper.readValue(record.key(), JsonNode.class));
        }
        if (record.value() != null) {
            node.set("value", mapper.readValue(record.value(), JsonNode.class));
        }
        if (includeMetadata) {
            node.putObject("metadata")
                .put("offset", record.offset())
                .put("topic", record.topic())
                .put("partition", record.partition());
        }

-------------------

Flink 的  FlinkKafkaConsumer、FlinkKafkaProducer，在消费、生成kafka 数据的时候，不能指定key，又时候，我们又需要这个key。

val kafkaSource = new FlinkKafkaConsumer[ObjectNode]("kafka_demo", new JsonNodeDeserializationSchema(), Common.getProp)
    val sink = new FlinkKafkaProducer[String]("kafka_demo_out", new SimpleStringSchema(), Common.getProp)
    sink.setWriteTimestampToKafka(true)

    env.addSource(kafkaSource)
      .map(node => {
        node.put("token", System.currentTimeMillis())
        node.toString
      })
      .addSink(sink)

下面通过flink 的自定source、sink 实现，消费、生成kafka 数据的时候，获取数据的key ，和输出不同key的数据

思路： 使用kafka 原生的api，KafkaConsuemr和KafkaProducer 消费、生产kafka的数据，就可以获取到key值

kafka 生产者：

object KafkaKeyMaker {
  val topic = "kafka_key"
  def main(args: Array[String]): Unit = {

    val producer = new KafkaProducer[String, String](Common.getProp)
    while (true) {
      val map = Map("user"->"venn", "name"->"venn","pass"->System.currentTimeMillis())
      val jsonObject: JSONObject = new JSONObject(map)
      println(jsonObject.toString())
      // key : msgKey + long
      val msg = new ProducerRecord[String, String](topic, "msgKey" + System.currentTimeMillis(), jsonObject.toString())
      producer.send(msg)
      producer.flush()
      Thread.sleep(3000)
    }

  }
}

kafka 消费者：

object KafkaKeyReceive{
  val topic = "kafka_key"
  def main(args: Array[String]): Unit = {
    val consumer = new KafkaConsumer[String, String](Common.getProp)
    consumer.subscribe(util.Arrays.asList(topic + "_out"))
    while (true) {
      val records = consumer.poll(500)
      val tmp = records.iterator()
      while (tmp.hasNext){
        val record = tmp.next()
        val key = record.key()
        val value = record.value()
        println("receive -> key : " + key + ", value : " + value)
      }
      Thread.sleep(3000)
    }
  }
}

flink 代码，自定义source、sink

import com.venn.common.Common
import org.apache.flink.api.scala._
import org.apache.flink.configuration.Configuration
import org.apache.flink.streaming.api.functions.sink.{RichSinkFunction, SinkFunction}
import org.apache.flink.streaming.api.functions.source.{RichSourceFunction, SourceFunction}
import org.apache.flink.streaming.api.scala.StreamExecutionEnvironment
import org.apache.kafka.clients.consumer.KafkaConsumer
import org.apache.kafka.clients.producer.{KafkaProducer, ProducerRecord}
import scala.collection.JavaConversions._
/**
  * Created by venn on 19-4-26.
  */
object KafkaSourceKey {

  def main(args: Array[String]): Unit = {
    // environment
    val env: StreamExecutionEnvironment = StreamExecutionEnvironment.getExecutionEnvironment

    
    env.addSource(new RichSourceFunction[String] {
      // kafka consumer 对象
      var consumer: KafkaConsumer[String, String] = null

      // 初始化方法
      override def open(parameters: Configuration): Unit = {
        consumer = new KafkaConsumer[String, String](Common.getProp)
        // 订阅topic
        val list = List("kafka_key")
        consumer.subscribe(list)
      }
      // 执行方法，拉取数据，获取到的数据，会放到source 的缓冲区
      override def run(ctx: SourceFunction.SourceContext[String]): Unit = {
        println("run")
        while (true) {
          val records = consumer.poll(500)
          val tmp = records.iterator()
          while (tmp.hasNext) {
            val record = tmp.next()
            val key = record.key()
            val value = record.value()

            ctx.collect("key : " + key + ", value " + value)
          }
        }

      }

      override def cancel(): Unit = {

        println("cancel")
      }
    }).map(s => s + "map")
      .addSink(new RichSinkFunction[String] {
        // kafka producer 对象
        var producer: KafkaProducer[String, String] = null

        // 初始化
        override def open(parameters: Configuration): Unit = {
          producer = new KafkaProducer[String, String](Common.getProp)
        }

        override def close(): Unit = {
          if (producer == null) {
            producer.flush()
            producer.close()
          }
        }

        // 输出数据，每条结果都会执行一次，并发高的时候，可以按需做flush
        override def invoke(value: String, context: SinkFunction.Context[_]): Unit = {

          println("flink : " + value)

          val msg = new ProducerRecord[String, String]( "kafka_key_out", "key" + System.currentTimeMillis(), value)
          producer.send(msg)
          producer.flush()
        }
      })
    // execute job
    env.execute("KafkaToKafka")
  }

}

kafka 生产者数据：

{"user" : "venn", "name" : "venn", "pass" : 1561355358148}
{"user" : "venn", "name" : "venn", "pass" : 1561355361271}
{"user" : "venn", "name" : "venn", "pass" : 1561355364276}
{"user" : "venn", "name" : "venn", "pass" : 1561355367279}
{"user" : "venn", "name" : "venn", "pass" : 1561355370283}

flink 输出数据：

run
flink : key : msgKey1561355358180, value {"user" : "venn", "name" : "venn", "pass" : 1561355358148}map
flink : key : msgKey1561355361271, value {"user" : "venn", "name" : "venn", "pass" : 1561355361271}map
flink : key : msgKey1561355364276, value {"user" : "venn", "name" : "venn", "pass" : 1561355364276}map
flink : key : msgKey1561355367279, value {"user" : "venn", "name" : "venn", "pass" : 1561355367279}map
flink : key : msgKey1561355370283, value {"user" : "venn", "name" : "venn", "pass" : 1561355370283}map
flink : key : msgKey1561355373289, value {"user" : "venn", "name" : "venn", "pass" : 1561355373289}map
flink : key : msgKey1561355376293, value {"user" : "venn", "name" : "venn", "pass" : 1561355376293}map

kafka 消费者：

receive -> key : key1561355430411, value : key : msgKey1561355430356, value {"user" : "venn", "name" : "venn", "pass" : 1561355430356}map
receive -> key : key1561355433427, value : key : msgKey1561355433359, value {"user" : "venn", "name" : "venn", "pass" : 1561355433359}map
receive -> key : key1561355436441, value : key : msgKey1561355436364, value {"user" : "venn", "name" : "venn", "pass" : 1561355436364}map
receive -> key : key1561355439456, value : key : msgKey1561355439367, value {"user" : "venn", "name" : "venn", "pass" : 1561355439367}map
receive -> key : key1561355442473, value : key : msgKey1561355442370, value {"user" : "venn", "name" : "venn", "pass" : 1561355442370}map
receive -> key : key1561355445391, value : key : msgKey1561355445374, value {"user" : "venn", "name" : "venn", "pass" : 1561355445374}map

注：这样设计有个问题，没办法做到精确一次：

　　1、source 的精确一次可以使用kafka 的低级api，每次从指定的offset 读取数据，提交新的offset，然后将当前的offset 存到状态中，这样即使程序失败，重启到上一个checkpoint状态，数据也不会重复。

　　2、sink 的处理比较麻烦，以官网介绍的 “两段提交”的方法，提交生产者的数据。简单来说，就是每次数据处理完后，需要提交数据到kafka，不做真正的提交，仅写入一些已定义的状态变量，当chckpoint成功时Flink负责提交这些写入，否则就终止取消掉。

参考zhisheng 大佬的 博客 ： 《从0到1学习Flink》—— 如何自定义 Data Source ？

《从0到1学习Flink》—— 如何自定义 Data Sink ？

两段提交的一篇翻译： 【译】Flink + Kafka 0.11端到端精确一次处理语义的实现