springboot引入kafka

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什么是 Kafka？
Kafka 是一个分布式流处理平台，最初由 LinkedIn 开发，并于 2011 年开源。它用于构建实时数据管道和流应用，能够处理和分析流数据。

Kafka 的核心概念
Producer（生产者）：发送消息到 Kafka 主题。
Consumer（消费者）：从 Kafka 主题中读取消息。
Broker（代理）：Kafka 服务器，负责接收和存储消息。
Topic（主题）：消息分类的逻辑单元。
Partition（分区）：主题的物理分区，便于并行处理。
Offset（偏移量）：每条消息在分区中的唯一标识符。

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<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.kafka</groupId>
        <artifactId>spring-kafka</artifactId>
    </dependency>
</dependencies>

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spring:
  kafka:
    bootstrap-servers: localhost:9092
    consumer:
      key-deserializer: org.apache.kafka.common.serialization.StringDeserializer
      value-deserializer: org.apache.kafka.common.serialization.StringDeserializer
      group-id: default-group  # 默认的消费者组
    consumer-group-1:
      group-id: group1
      topic: topic1
    consumer-group-2:
      group-id: group2
      topic: topic2
    producer:
      key-serializer: org.apache.kafka.common.serialization.StringSerializer
      value-serializer: org.apache.kafka.common.serialization.StringSerializer
    template:
      default-topic: my-topic

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 import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.common.serialization.StringDeserializer;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.kafka.annotation.EnableKafka;
import org.springframework.kafka.config.ConcurrentKafkaListenerContainerFactory;
import org.springframework.kafka.core.ConsumerFactory;
import org.springframework.kafka.core.DefaultKafkaConsumerFactory;

import java.util.HashMap;
import java.util.Map;

@EnableKafka
@Configuration
public class KafkaConsumerConfig {

    @Value("${spring.kafka.bootstrap-servers}")
    private String bootstrapServers;

    @Value("${spring.kafka.consumer.key-deserializer}")
    private String keyDeserializer;

    @Value("${spring.kafka.consumer.value-deserializer}")
    private String valueDeserializer;

    @Bean
    public Map<String, Object> consumerConfigs() {
        Map<String, Object> props = new HashMap<>();
        props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, bootstrapServers);
        props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, keyDeserializer);
        props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, valueDeserializer);
        props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");
        return props;
    }

    @Bean
    public ConsumerFactory<String, String> consumerFactory() {
        return new DefaultKafkaConsumerFactory<>(consumerConfigs());
    }

    @Bean(name = "kafkaListenerContainerFactoryGroup1")
    public ConcurrentKafkaListenerContainerFactory<String, String> kafkaListenerContainerFactoryGroup1(
            @Value("${spring.kafka.consumer-group-1.group-id}") String groupId) {
        return createFactory(groupId);
    }

    @Bean(name = "kafkaListenerContainerFactoryGroup2")
    public ConcurrentKafkaListenerContainerFactory<String, String> kafkaListenerContainerFactoryGroup2(
            @Value("${spring.kafka.consumer-group-2.group-id}") String groupId) {
        return createFactory(groupId);
    }

    private ConcurrentKafkaListenerContainerFactory<String, String> createFactory(String groupId) {
        ConcurrentKafkaListenerContainerFactory<String, String> factory = new ConcurrentKafkaListenerContainerFactory<>();
        Map<String, Object> props = new HashMap<>(consumerConfigs());
        props.put(ConsumerConfig.GROUP_ID_CONFIG, groupId);
        factory.setConsumerFactory(new DefaultKafkaConsumerFactory<>(props));
        return factory;
    }
}

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auto.offset.reset 配置选项
earliest：当没有初始偏移量或者当前偏移量超出范围时，消费者将从最早的可用数据开始读取。这通常用于新消费者加入时，从头开始读取所有历史数据。
latest：当没有初始偏移量或者当前偏移量超出范围时，消费者将从最新的数据开始读取。这通常用于新消费者加入时，只读取从现在开始的数据。
none：如果消费者没有找到当前偏移量或偏移量超出范围，则会抛出异常。这要求消费者必须有有效的偏移量。
anything else：其他值将导致消费者抛出异常。

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import org.springframework.kafka.annotation.KafkaListener;
import org.springframework.stereotype.Service;

@Service
public class KafkaConsumerService {

    @KafkaListener(topics = "${spring.kafka.consumer-group-1.topic}", containerFactory = "kafkaListenerContainerFactoryGroup1")
    public void listenGroup1(String message) {
        System.out.println("Received message in group1: " + message);
    }

    @KafkaListener(topics = "${spring.kafka.consumer-group-2.topic}", containerFactory = "kafkaListenerContainerFactoryGroup2")
    public void listenGroup2(String message) {
        System.out.println("Received message in group2: " + message);
    }
}

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import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class KafkaProducerController {

    @Autowired
    private KafkaTemplate<String, String> kafkaTemplate;

    @GetMapping("/send")
    public String sendMessage(@RequestParam("message") String message) {
        kafkaTemplate.send("my-topic", message);
        return "Message sent to Kafka topic";
    }
}