kafka producer的serializer

今天遇到问题，kafka的producer是的类型，却始终报错，

[2015-01-14 15:10:22,837] ERROR Error serializing message for topic haidafu (kafka.producer.async.DefaultEventHandler)
java.lang.ClassCastException: java.lang.String cannot be cast to [B

找了半天问题，从网上搜到解决办法，原来kafka的producer有两种serializer，需要和producer的类型配合使用，特转载到这里

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Kafka错误java.lang.String cannot be cast to [B

向kafka发送数据，默认支持String和byte[]2种类型，如何支持呢？serializer是关键。kafka默认包括kafka.serializer.StringEncoder
和kafka.serializer.DefaultEncoder 2个类，分别支持String和二进制。在创建Producer时，需要配置参数props.put("serializer.class", "kafka.serializer.StringEncoder");

KeyedMessage将需要发送的进行封装，根据定义的serializer.class，定义不同的KeyedMessage

如果需要发送字符串，方式如下：

import java.util.Properties;
import kafka.javaapi.producer.Producer;
import kafka.producer.KeyedMessage;
import kafka.producer.ProducerConfig;

//创建Producer
Properties props = new Properties();
props.put("metadata.broker.list", "192.168.1.1:9092,192.168.1.2:9092 ");
props.put("serializer.class", "kafka.serializer.StringEncoder");
props.put("producer.type", "sync");
//props.put("reconnect.time.interval.ms", 5*1000);
props.put("request.required.acks", "1");
//props.put("compression.codec", "gzip");

ProducerConfig config = new ProducerConfig(props);
Producer producer = new Producer(config);

//发送数据

String message = "hello message";
//KeyedMessage 第一个String是key的类型，第二个String是value类型
//可以用key来进行Hash，发送message到不同的分区

KeyedMessage keymsg = new KeyedMessage("mytopic",message);
//这里的KeyedMessage没有key值

producer.send(keymsg);


发送二进制消息，方式类似，需要修改serializer.class，和key.serializer.class配置

import java.util.Properties;
import kafka.javaapi.producer.Producer;
import kafka.producer.KeyedMessage;
import kafka.producer.ProducerConfig;



//创建Producer
Properties props = new Properties();
props.put("metadata.broker.list", "192.168.1.1:9092,192.168.1.2:9092 ");
props.put("serializer.class", "kafka.serializer.DefaultEncoder");
//key的类型需要和serializer保持一致，如果key是String，则需要配置为kafka.serializer.StringEncoder，如果不配置，默认为kafka.serializer.DefaultEncoder，即二进制格式
props.put("key.serializer.class", "kafka.serializer.StringEncoder");
props.put("producer.type", "sync");
//props.put("reconnect.time.interval.ms", 5*1000);
props.put("request.required.acks", "1");
//props.put("compression.codec", "gzip");

ProducerConfig config = new ProducerConfig(props);
Producer producer = new Producer(config);

//发送数据

String message = "hello message";
//KeyedMessage 第一个String是key的类型，第二个byte[]是value类型
//可以用key来进行Hash，发送message到不同的分区

KeyedMessage keymsg = new KeyedMessage("mytopic",message.getBytes());
//这里的KeyedMessage没有key值

producer.send(keymsg);

如果serializer.class或key.serializer.class配置不正确，就会报如下错误

java.lang.ClassCastException: java.lang.String cannot be cast to [B
at kafka.serializer.DefaultEncoder.toBytes(Encoder.scala:34)
at kafka.producer.async.DefaultEventHandler$$anonfun$serialize$1.apply(DefaultEventHandler.scala:128)
at kafka.producer.async.DefaultEventHandler$$anonfun$serialize$1.apply(DefaultEventHandler.scala:125)
at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:233)
at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:233)
at scala.collection.Iterator$class.foreach(Iterator.scala:772)
at scala.collection.JavaConversions$JIteratorWrapper.foreach(JavaConversions.scala:573)
at scala.collection.IterableLike$class.foreach(IterableLike.scala:73)
at scala.collection.JavaConversions$JListWrapper.foreach(JavaConversions.scala:615)
at scala.collection.TraversableLike$class.map(TraversableLike.scala:233)
at scala.collection.JavaConversions$JListWrapper.map(JavaConversions.scala:615)
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:76)
at kafka.javaapi.producer.Producer.send(Producer.scala:42)