Kafka--JAVA API（Producer和Consumer）

Kafka 版本2.11-0.9.0.0

producer

package com.yzy.spark.kafka;

import kafka.javaapi.producer.Producer;
import kafka.producer.KeyedMessage;

import kafka.producer.ProducerConfig;

import java.util.Properties;

/**
 * Producer
 */
public class KafkaProducer extends Thread{
    private String topic;
    //--1
    private Producer<String, String> producer;
    public KafkaProducer(String topic){
        this.topic=topic;

        Properties properties = new Properties(); //--2
        properties.put("metadata.broker.list",KafkaProperties.BROKER_LIST);
        properties.put("serializer.class","kafka.serializer.StringEncoder");
        properties.put("request.require.acks","1");
//        properties.put("partitioner.class","com.yzy.spark.kafka.MyPartition");
        ProducerConfig config=new ProducerConfig(properties);
        producer=new Producer<>(config);
    }

    @Override
    public void run() {
        int messageNo=1;
        while (true){
            String message="message"+ messageNo;
            producer.send(new KeyedMessage<String,String>("test2",String.valueOf(messageNo),message)); //--4
            System.out.println("Sent:"+message);
            messageNo++;
            try {
                Thread.sleep(1000);
            }catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

1.定义Producer<K,V>对象，这里要注意泛型类型，之后的KeyedMessage<K,V>的泛型类型和Producer<K,V>相同。

2.创建Producer<K,V>对象需要传入一个ProducerConfig对象，而ProducerConfig对象需要由Properties对象构造，properties的属性设置可以查看ProducerConfig源码，注释很详细（个别属性在ProducerConfig父类AsyncProducerConfig 和 SyncProducerConfigShared中）。

3.该属性可以指定partitioner，如果不设置默认会设为kafka.producer.DefaultPartitioner。

4.看看KeyedMessage的源码：

case class KeyedMessage[K, V](topic: String, key: K, partKey: Any, message: V) {
  if(topic == null)
    throw new IllegalArgumentException("Topic cannot be null.")
  
  def this(topic: String, message: V) = this(topic, null.asInstanceOf[K], null, message)
  
  def this(topic: String, key: K, message: V) = this(topic, key, key, message)
  
  def partitionKey = {
    if(partKey != null)
      partKey
    else if(hasKey)
      key
    else
      null  
  }
  
  def hasKey = key != null
}

参数有4个，topic必填，message是消息，通常只填这两个参数即可发送消息。key和partKey是用于partition的参数，partKey的优先级高于key，但是partKey只对当前消息起作用，key和partKey只能是String类型。下面来看看partition策略和key。

partition

先在服务器端将topic test2的partitions设定为3

kafka-topics.sh --alter --zookeeper localhost:2181 --partitions 3 --topic test2

然后回到客户端看看kafka.producer.DefaultPartitioner源码


package kafka.producer


import kafka.utils._
import org.apache.kafka.common.utils.Utils

class DefaultPartitioner(props: VerifiableProperties = null) extends Partitioner {
  private val random = new java.util.Random
  
  def partition(key: Any, numPartitions: Int): Int = {
    Utils.abs(key.hashCode) % numPartitions
  }
}

该类有一个方法 def partition(key: Any, numPartitions: Int)，第一个参数为上文所说的key或partKey，第二个为partitions的数量，传入的值就是在服务器设置的值（3），将key的hashCode对numPartitions取余得到结果（选择对应编号的partition）

我们可以自己定义一个partition.class并配置到properties属性中，这里给一个简单的例子：

package com.yzy.spark.kafka;

import kafka.producer.Partitioner;
import kafka.utils.VerifiableProperties;

public class MyPartition implements Partitioner {
    public MyPartition(VerifiableProperties properties){

    }
    @Override
    public int partition(Object key, int numPartitions) {
        System.out.println("numPartitions:"+numPartitions);
        return key.hashCode()%numPartitions;

    }
}

Consumer

package com.yzy.spark.kafka;

import kafka.consumer.Consumer;
import kafka.consumer.ConsumerConfig;
import kafka.consumer.ConsumerIterator;
import kafka.consumer.KafkaStream;
import kafka.javaapi.consumer.ConsumerConnector;

import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Properties;

public class KafkaConsumer extends Thread{
    private String topic;
    private String groupId;

    public KafkaConsumer(String topic,String groupId){
        this.topic=topic;
        this.groupId=groupId;
        
    }

    private ConsumerConnector createConnector(){
        Properties properties=new Properties();//--1
        properties.put("zookeeper.connect",KafkaProperties.ZK);
        properties.put("group.id",groupId);
        properties.put("auto.offset.reset", "largest");//--2
        ConsumerConfig consumerConfig = new ConsumerConfig(properties);
        return Consumer.createJavaConsumerConnector(consumerConfig);
    }

    @Override
    public void run() {
        ConsumerConnector consumerConnector=this.createConnector();
        Map<String,Integer> topicCountMap=new HashMap<>();
        topicCountMap.put(topic,1);
        Map<String, List<KafkaStream<byte[], byte[]>>> messageStreams = consumerConnector.createMessageStreams(topicCountMap);
        KafkaStream<byte[], byte[]> stream = messageStreams.get(topic).get(0);
        ConsumerIterator<byte[], byte[]> iterator = stream.iterator();

        while(iterator.hasNext()){
            String message=new String(iterator.next().message());
        }
    }
}

Consumer相关的东西比较多，涉及到group和partition机制，以官方文档为准。

1.properties和producer一样看源码配置。

2.这个属性和shell命令中的--from-beginning对应。可以填smallest（从头读取）和largest（默认值，读取最新的元素，严格来说是最新的offset位置开始读取）。注意：每一次一个新的consumer试图去消费一个topic时，都是从所在group的largest offset位置读取，即也可通过设置group.id来实现from-beginning，只要将每个consumer的group.id都设置为一个新值即可，例如properties.put("group.id", UUID.randomUUID().toString());

Kafka-JavaAPI(Producer And Consumer)

Kafka--JAVA API（Producer和Consumer）

producer

partition

Consumer

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