Kafka-0.8.2.x Consumer API

摘要

本文主要说下此版本消费者API重要的一些代码含义。

0x01 完整例子

1.1 Consumer消费代码

class ConsumerTest implements Runnable {
    private KafkaStream m_stream;
    private int m_threadNumber;
 
    public ConsumerTest(KafkaStream a_stream, int a_threadNumber) {
        m_threadNumber = a_threadNumber;
        m_stream = a_stream;
    }
 
    public void run() {
        // Consumer线程只需要使用iterator遍历该消息，进行业务逻辑处理即可
        ConsumerIterator<byte[], byte[]> it = m_stream.iterator();
        while (it.hasNext())
            System.out.println("Thread " + m_threadNumber + ": " + new String(it.next().message()));
        System.out.println("Shutting down Thread: " + m_threadNumber);
    }
}

1.2 构建消费者、main函数等代码

package com.test.groups;
 
import kafka.consumer.ConsumerConfig;
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;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
 
public class ConsumerGroupExample {
    private final ConsumerConnector consumer;
    private final String topic;
    private  ExecutorService executor;
 
    public ConsumerGroupExample(String a_zookeeper, String a_groupId, String a_topic) {
        // 通过配置构建一个KafkaConsumer实例
        consumer = kafka.consumer.Consumer.createJavaConsumerConnector(
                createConsumerConfig(a_zookeeper, a_groupId));
        this.topic = a_topic;
    }
 
    public void shutdown() {
        if (consumer != null) consumer.shutdown();
        if (executor != null) executor.shutdown();
        try {
            if (!executor.awaitTermination(5000, TimeUnit.MILLISECONDS)) {
                System.out.println("Timed out waiting for consumer threads to shut down, exiting uncleanly");
            }
        } catch (InterruptedException e) {
            System.out.println("Interrupted during shutdown, exiting uncleanly");
        }
   }
 
    public void run(int a_numThreads) {
        Map<String, Integer> topicCountMap = new HashMap<String, Integer>();
        // 确定一个Consumer实例对于指定的topic拥有几个线程来处理
        topicCountMap.put(topic, new Integer(a_numThreads));
        // 通过topicCountMap构建消息流
        Map<String, List<KafkaStream<byte[], byte[]>>> consumerMap = consumer.createMessageStreams(topicCountMap);
        // 对指定topic构建消息流list
        List<KafkaStream<byte[], byte[]>> streams = consumerMap.get(topic);
 
        // 创建一个指定线程数量的线程池
        executor = Executors.newFixedThreadPool(a_numThreads);
 
        // 遍历消息流，每个都创建一个消费者线程提交到线程池进行处理
        int threadNumber = 0;
        for (final KafkaStream stream : streams) {
            executor.submit(new ConsumerTest(stream, threadNumber));
            threadNumber++;
        }
    }
    
    /**
     * 构建Consumer基础配置
     */
    private static ConsumerConfig createConsumerConfig(String a_zookeeper, String a_groupId) {
        Properties props = new Properties();
        props.put("zookeeper.connect", a_zookeeper);
        props.put("group.id", a_groupId);
        props.put("zookeeper.session.timeout.ms", "400");
        props.put("zookeeper.sync.time.ms", "200");
        props.put("auto.commit.interval.ms", "1000");
 
        return new ConsumerConfig(props);
    }
 
    public static void main(String[] args) {
        String zooKeeper = args[0];
        String groupId = args[1];
        String topic = args[2];
        // 消费者线程数
        int threads = Integer.parseInt(args[3]);
 
        ConsumerGroupExample example = new ConsumerGroupExample(zooKeeper, groupId, topic);
        example.run(threads);
 
        try {
            Thread.sleep(10000);
        } catch (InterruptedException ie) {
 
        }
        example.shutdown();
    }
}

0x02 一些需要注意的点

2.1 消费者线程数配置

topicCountMap.put(topic, new Integer(a_numThreads));

• 使用topicCountMap配置topic线程数的时候，这个是针对同一个组的一个消费者实例的。如果总的线程数大于了partition数量 ，那就会导致一些线程不会消费任何数据。
• 反过来，如果partitions数大于线程数，那么一些线程会同时接收多个partition数据。注意此时仍然只能保证一个partition内部有序。
• 当添加更多Consumer实例或线程时会导致Kafka再平衡，可能影响parition分配给线程的策略。

0xFF 参考文档

Consumer Group Example