問題描述

在網上都只看到一些Java生產STRING類型的消息。 按照Java的producer類來看，是可以自定義發送消息的類型，比如 producer.send(new KeyedMessage<String, HashMap<String , String>>(topic,message); 可是這樣運行會報錯，報錯如下，請求高人解答：Exception in thread 'Thread-4' java.lang.ClassCastException: java.util.HashMap cannot be cast to java.lang.String

at kafka.serializer.StringEncoder.toBytes(Encoder.scala:46)at kafka.producer.async.DefaultEventHandler$$anonfun$serialize$1.apply(DefaultEventHandler.scala:130)at kafka.producer.async.DefaultEventHandler$$anonfun$serialize$1.apply(DefaultEventHandler.scala:125)at scala.collection.IndexedSeqOptimized$class.foreach(IndexedSeqOptimized.scala:33)at scala.collection.mutable.WrappedArray.foreach(WrappedArray.scala:34)at kafka.producer.async.DefaultEventHandler.serialize(DefaultEventHandler.scala:125)at kafka.producer.async.DefaultEventHandler.handle(DefaultEventHandler.scala:52)at kafka.producer.Producer.send(Producer.scala:77)at kafka.javaapi.producer.Producer.send(Producer.scala:33)at com.Model.Producer.kafkaProducer.run(kafkaProducer.java:35)

問題解答

文檔，序列化成String就行了