作为 kafka 消费者同时消费多个主题

Question

我正在关注这个 url https://cwiki.apache.org/confluence/display/KAFKA/Consumer+Group+Example 中关于并发消费 kafka 主题的示例。

在创建线程池部分，他们有以下代码

public void run(int a_numThreads) {
    Map<String, Integer> topicCountMap = new HashMap<String, Integer>();
    topicCountMap.put(topic, new Integer(a_numThreads));
    Map<String, List<KafkaStream<byte[], byte[]>>> consumerMap = consumer.createMessageStreams(topicCountMap);
    List<KafkaStream<byte[], byte[]>> streams = consumerMap.get(topic);


    // now launch all the threads
    //
    executor = Executors.newFixedThreadPool(a_numThreads);

    // now create an object to consume the messages
    //
    int threadNumber = 0;
    for (final KafkaStream stream : streams) {
        executor.submit(new ConsumerTest(stream, threadNumber));
        threadNumber++;
    }
}

我可以向 topicCountMap 添加更多主题。 例如，

topicCountMap.put("channel1", new Integer(a_numThreads));
topicCountMap.put("channe2", new Integer(a_numThreads));
topicCountMap.put("channel3", new Integer(a_numThreads));

在上面的代码中，在我看来，流对象只映射到主题之一

List<KafkaStream<byte[], byte[]>> streams = consumerMap.get(topic);

我不完全确定如何创建多个流对象，每个对象都映射到给定的主题，然后遍历它们以从每个通道获取数据并将它们提交给执行程序。

Answer 1

假设你有：

String topic1 = "channel1";
String topic2 = "channel2";
String topic3 = "channel3";

然后，你确实可以这样做：

topicCountMap.put(topic1, new Integer(a_numThreads_topic1));
topicCountMap.put(topic2, new Integer(a_numThreads_topic2));
topicCountMap.put(topic3, new Integer(a_numThreads_topic3));

一旦您获得了您的 consumerMap（执行此操作的代码不会改变），您将能够检索每个主题的流：

List<KafkaStream<byte[], byte[]>> topic1_streams = consumerMap.get(topic1);
List<KafkaStream<byte[], byte[]>> topic2_streams = consumerMap.get(topic2);
List<KafkaStream<byte[], byte[]>> topic3_streams = consumerMap.get(topic3);

要从流中使用，您需要创建正确数量的执行程序：

executors_topic1 = Executors.newFixedThreadPool(a_numThreads_topic1);
executors_topic2 = Executors.newFixedThreadPool(a_numThreads_topic2);
executors_topic3 = Executors.newFixedThreadPool(a_numThreads_topic3);

最后 ：

int threadNumber = 0;
for (final KafkaStream stream : topic1_streams) {
    executors_topic1.submit(new ConsumerTest(streams, threadNumber));
    threadNumber++;
}
for (final KafkaStream stream : topic2_streams) {
    executors_topic2.submit(new ConsumerTest(stream, threadNumber));
    threadNumber++;
}
for (final KafkaStream stream : topic3_streams) {
    executor_topic3.submit(new ConsumerTest(stream, threadNumber));
    threadNumber++;
}

当然，这只是给你的想法。 显然，代码可以改进。