kafka复习：（22）一个分区只能被消费者组中的一个消费者消费吗？

默认情况下，一个分区只能被消费者组中的一个消费者消费。但可以自定义PartitionAssignor来打破这个限制。
一、自定义PartitionAssignor.

package com.cisdi.dsp.modules.metaAnalysis.rest.kafka2023;

import org.apache.kafka.clients.consumer.internals.AbstractPartitionAssignor;
import org.apache.kafka.common.TopicPartition;

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

public class BroadcastAssignor extends AbstractPartitionAssignor {
    @Override
    public String name() {
        return "broadcast";
    }

    private Map<String, List<String>> consumersPerTopic(Map<String, Subscription> consumerMetadata) {
        Map<String, List<String>> res = new HashMap<>();
        for (Map.Entry<String, Subscription> subscriptionEntry : consumerMetadata.entrySet()) {
            String consumerId = subscriptionEntry.getKey();
            for (String topic : subscriptionEntry.getValue().topics())
                put(res, topic, consumerId);
        }
        return res;
    }

    @Override
    public Map<String, List<TopicPartition>> assign(
            Map<String, Integer> partitionsPerTopic,
            Map<String, Subscription> subscriptions) {
        Map<String, List<String>> consumersPerTopic =
                consumersPerTopic(subscriptions);
        Map<String, List<TopicPartition>> assignment = new HashMap<>();
        subscriptions.keySet().forEach(memberId ->
                assignment.put(memberId, new ArrayList<>()));
        consumersPerTopic.entrySet().forEach(topicEntry->{
            String topic = topicEntry.getKey();
            List<String> members = topicEntry.getValue();

            Integer numPartitionsForTopic = partitionsPerTopic.get(topic);
            if (numPartitionsForTopic == null || members.isEmpty())
                return;
            List<TopicPartition> partitions = AbstractPartitionAssignor
                    .partitions(topic, numPartitionsForTopic);
            if (!partitions.isEmpty()) {
                members.forEach(memberId ->
                        assignment.get(memberId).addAll(partitions));
            }
        });
        return assignment;
    }
}

二、定义两个消费者，给其配置上述PartitionAssignor.

package com.cisdi.dsp.modules.metaAnalysis.rest.kafka2023;

import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import org.apache.kafka.clients.producer.ProducerConfig;
import org.apache.kafka.common.TopicPartition;
import org.apache.kafka.common.serialization.StringDeserializer;
import org.apache.kafka.common.serialization.StringSerializer;

import java.time.Duration;
import java.time.temporal.TemporalUnit;
import java.util.Arrays;
import java.util.Properties;
import java.util.concurrent.TimeUnit;

public class KafkaTest19 {

    private static Properties getProperties(){
        Properties properties=new Properties();

        properties.setProperty(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());
        properties.setProperty(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());
        properties.setProperty(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG,"xx.xx.xx.xx:9092");
        properties.setProperty(ConsumerConfig.GROUP_ID_CONFIG,"testGroup2023");
        properties.setProperty(ConsumerConfig.PARTITION_ASSIGNMENT_STRATEGY_CONFIG,
                BroadcastAssignor.class.getName());
        return properties;
    }
    public static void main(String[] args) {

        KafkaConsumer<String,String> myConsumer=new KafkaConsumer<String, String>(getProperties());
        String topic="study2023";
        myConsumer.subscribe(Arrays.asList(topic));

        while(true){
            ConsumerRecords<String,String> consumerRecords=myConsumer.poll(Duration.ofMillis(5000));
            for(ConsumerRecord record: consumerRecords){
                System.out.println(record.value());
                System.out.println("record offset is: "+record.offset());
            }

        }

    }
}

package com.cisdi.dsp.modules.metaAnalysis.rest.kafka2023;

import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import org.apache.kafka.clients.producer.ProducerConfig;
import org.apache.kafka.common.TopicPartition;
import org.apache.kafka.common.serialization.StringDeserializer;
import org.apache.kafka.common.serialization.StringSerializer;

import java.time.Duration;
import java.time.temporal.TemporalUnit;
import java.util.Arrays;
import java.util.Properties;
import java.util.concurrent.TimeUnit;

public class KafkaTest20 {

    private static Properties getProperties(){
        Properties properties=new Properties();

        properties.setProperty(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());
        properties.setProperty(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());
        properties.setProperty(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG,"xx.xx.xx.xx:9092");
        properties.setProperty(ConsumerConfig.GROUP_ID_CONFIG,"testGroup2023");
        properties.setProperty(ConsumerConfig.PARTITION_ASSIGNMENT_STRATEGY_CONFIG,
                BroadcastAssignor.class.getName());
        return properties;
    }
    public static void main(String[] args) {

        KafkaConsumer<String,String> myConsumer=new KafkaConsumer<String, String>(getProperties());
        String topic="study2023";
        myConsumer.subscribe(Arrays.asList(topic));

        while(true){
            ConsumerRecords<String,String> consumerRecords=myConsumer.poll(Duration.ofMillis(5000));
            for(ConsumerRecord record: consumerRecords){
                System.out.println(record.value());
                System.out.println("record offset is: "+record.offset());
            }

        }

    }
}

在kafka创建只有一个分区的topic ： study2023

创建一个生产者往study2023这个 topic发送消息：

package com.cisdi.dsp.modules.metaAnalysis.rest.kafka2023;

import org.apache.kafka.clients.producer.KafkaProducer;
import org.apache.kafka.clients.producer.ProducerConfig;
import org.apache.kafka.clients.producer.ProducerRecord;
import org.apache.kafka.clients.producer.RecordMetadata;
import org.apache.kafka.common.serialization.StringSerializer;

import java.util.Date;
import java.util.Properties;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;

public class KafkaTest01 {
    public static void main(String[] args) {
        Properties properties= new Properties();

        properties.setProperty(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class.getName());
        properties.setProperty(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class.getName());
        properties.setProperty(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG,"xx.xx.xx.xx:9092");
        KafkaProducer<String,String> kafkaProducer=new KafkaProducer<String, String>(properties);
        ProducerRecord<String,String> producerRecord=new ProducerRecord<>("study2023",0,"fff","hello sister,now is: "+ new Date());
        Future<RecordMetadata> future = kafkaProducer.send(producerRecord);
        long offset = 0;
        try {
            offset = future.get().offset();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
        System.out.println(offset);

        kafkaProducer.close();
    }
}

分别运行生产者和消费者，可以看到相同消费者组里两个消费者可以消费study2023这个topic的同一个分区的数据