Spring Boot 集成 Kafka

Spring Boot 与 Kafka 集成是实现高效消息传递和数据流处理的常见方式。Spring Boot 提供了简化 Kafka 配置和使用的功能，使得集成过程变得更加直观和高效。以下是 Spring Boot 集成 Kafka 的详细步骤，包括配置、生产者和消费者的实现以及一些高级特性。

1. 添加依赖

首先，你需要在 Spring Boot 项目的 pom.xml 文件中添加 Kafka 相关的依赖。使用 Spring Boot 的起步依赖可以简化配置。

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-kafka</artifactId>
</dependency>
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2. 配置 Kafka

2.1. 配置文件

在 application.properties 或 application.yml 文件中配置 Kafka 相关属性。

application.properties:

# Kafka 服务器地址
spring.kafka.bootstrap-servers=localhost:9092

# Kafka 消费者配置
spring.kafka.consumer.group-id=my-group
spring.kafka.consumer.auto-offset-reset=earliest
spring.kafka.consumer.key-deserializer=org.apache.kafka.common.serialization.StringDeserializer
spring.kafka.consumer.value-deserializer=org.apache.kafka.common.serialization.StringDeserializer

# Kafka 生产者配置
spring.kafka.producer.key-serializer=org.apache.kafka.common.serialization.StringSerializer
spring.kafka.producer.value-serializer=org.apache.kafka.common.serialization.StringSerializer
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application.yml:

spring:
  kafka:
    bootstrap-servers: localhost:9092
    consumer:
      group-id: my-group
      auto-offset-reset: earliest
      key-deserializer: org.apache.kafka.common.serialization.StringDeserializer
      value-deserializer: org.apache.kafka.common.serialization.StringDeserializer
    producer:
      key-serializer: org.apache.kafka.common.serialization.StringSerializer
      value-serializer: org.apache.kafka.common.serialization.StringSerializer
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2.2. Kafka 配置类

在 Spring Boot 中，你可以使用 @Configuration 注解创建一个配置类，来定义 Kafka 的生产者和消费者配置。

import org.apache.kafka.clients.producer.ProducerConfig;
import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.common.serialization.StringDeserializer;
import org.apache.kafka.common.serialization.StringSerializer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.kafka.core.ConsumerFactory;
import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.kafka.core.ProducerFactory;
import org.springframework.kafka.core.DefaultKafkaConsumerFactory;
import org.springframework.kafka.core.DefaultKafkaProducerFactory;
import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.kafka.listener.ConcurrentMessageListenerContainer;
import org.springframework.kafka.listener.config.ContainerProperties;
import org.springframework.kafka.annotation.EnableKafka;
import org.springframework.kafka.config.ConcurrentKafkaListenerContainerFactory;
import org.springframework.kafka.core.ConsumerFactory;
import org.springframework.kafka.core.ProducerFactory;
import org.springframework.kafka.core.DefaultKafkaConsumerFactory;
import org.springframework.kafka.core.DefaultKafkaProducerFactory;

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

@Configuration
@EnableKafka
public class KafkaConfig {

    @Bean
    public ProducerFactory<String, String> producerFactory() {
        Map<String, Object> configProps = new HashMap<>();
        configProps.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
        configProps.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
        configProps.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
        return new DefaultKafkaProducerFactory<>(configProps);
    }

    @Bean
    public KafkaTemplate<String, String> kafkaTemplate() {
        return new KafkaTemplate<>(producerFactory());
    }

    @Bean
    public ConsumerFactory<String, String> consumerFactory() {
        Map<String, Object> configProps = new HashMap<>();
        configProps.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
        configProps.put(ConsumerConfig.GROUP_ID_CONFIG, "my-group");
        configProps.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
        configProps.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
        return new DefaultKafkaConsumerFactory<>(configProps);
    }

    @Bean
    public ConcurrentKafkaListenerContainerFactory<String, String> kafkaListenerContainerFactory() {
        ConcurrentKafkaListenerContainerFactory<String, String> factory =
                new ConcurrentKafkaListenerContainerFactory<>();
        factory.setConsumerFactory(consumerFactory());
        return factory;
    }
}
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3. 实现 Kafka 生产者

3.1. 生产者服务

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.stereotype.Service;

@Service
public class KafkaProducerService {

    @Autowired
    private KafkaTemplate<String, String> kafkaTemplate;

    private static final String TOPIC = "my_topic";

    public void sendMessage(String message) {
        kafkaTemplate.send(TOPIC, message);
    }
}
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3.2. 控制器示例

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class KafkaController {

    @Autowired
    private KafkaProducerService kafkaProducerService;

    @PostMapping("/send")
    public void sendMessage(@RequestBody String message) {
        kafkaProducerService.sendMessage(message);
    }
}
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4. 实现 Kafka 消费者

4.1. 消费者服务

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

@Service
public class KafkaConsumerService {

    @KafkaListener(topics = "my_topic", groupId = "my-group")
    public void listen(String message) {
        System.out.println("Received message: " + message);
    }
}
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5. 高级特性

5.1. 消息事务

Kafka 支持消息事务，确保消息的原子性。

生产者配置：

spring.kafka.producer.enable-idempotence=true
spring.kafka.producer.transaction-id-prefix=my-transactional-id
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使用事务：

import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.kafka.core.ProducerFactory;
import org.springframework.kafka.core.TransactionTemplate;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

@Service
public class KafkaTransactionalService {

    private final KafkaTemplate<String, String> kafkaTemplate;
    private final TransactionTemplate transactionTemplate;

    public KafkaTransactionalService(KafkaTemplate<String, String> kafkaTemplate, TransactionTemplate transactionTemplate) {
        this.kafkaTemplate = kafkaTemplate;
        this.transactionTemplate = transactionTemplate;
    }

    @Transactional
    public void sendMessageInTransaction(String message) {
        kafkaTemplate.executeInTransaction(t -> {
            kafkaTemplate.send("my_topic", message);
            return true;
        });
    }
}
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5.2. 异步发送与回调

异步发送：

public void sendMessageAsync(String message) {
    kafkaTemplate.send("my_topic", message).addCallback(
        result -> System.out.println("Sent message: " + message),
        ex -> System.err.println("Failed to send message: " + ex.getMessage())
    );
}
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总结

Spring Boot 与 Kafka 的集成使得消息队列的使用变得更加简单和高效。通过上述步骤，你可以轻松地配置 Kafka、实现生产者和消费者，并利用 Spring Boot 提供的强大功能来处理消息流。了解 Kafka 的高级特性（如事务和异步处理）能够帮助你更好地满足业务需求，确保系统的高可用性和数据一致性。