SpringBoot3 整合Kafka

官网：https://kafka.apache.org/documentation/

消息队列-场景

1. 异步

2. 解耦

3. 削峰

4. 缓冲

消息队列-Kafka

1. 消息模式

消息发布订阅模式，MessageQueue中的消息不删除，会记录消费者的偏移量

2. Kafka工作原理

同一个消费者组里的消费者是队列竞争模式：Consumer1消费Broker-0的news消息，Consumer2消费Broker-1的news消息，Consumer3消费Broker-2的news消息。如果有Consumer4，那他哪个分区都不能消费，就是消费的饥饿问题。

不同消费组中的消费者是发布/订阅模式：Consumer1和Consumer4都能消费0分区（Broker0）。

3. SpringBoot整合

参照：https://docs.spring.io/spring-kafka/docs/current/reference/html/#preface

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

配置

spring.kafka.bootstrap-servers=172.20.128.1:9092

修改C:\Windows\System32\drivers\etc\hosts文件，配置8.130.32.70 kafka

4. 消息发送

kafkaTemplate发送消息的内容是对象时，需要用json序列化，在配置文件中加上：

spring.kafka.producer.value-serializer=org.springframework.kafka.support.serializer.JsonSerializer

@SpringBootTest
class Boot07KafkaApplicationTests {

    @Autowired
    KafkaTemplate kafkaTemplate;
    @Test
    void contextLoads() throws ExecutionException, InterruptedException {
        StopWatch watch = new StopWatch();
        watch.start();
        CompletableFuture[] futures = new CompletableFuture[10000];
        for (int i = 0; i < 10000; i++) {
            CompletableFuture send = kafkaTemplate.send("order", "order.create."+i, "订单创建了："+i);
            futures[i]=send;
        }
        CompletableFuture.allOf(futures).join();
        watch.stop();
        System.out.println("总耗时："+watch.getTotalTimeMillis());
    }
}

import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

    private final KafkaTemplate<String, String> kafkaTemplate;

    public MyBean(KafkaTemplate<String, String> kafkaTemplate) {
        this.kafkaTemplate = kafkaTemplate;
    }

    public void someMethod() {
        this.kafkaTemplate.send("someTopic", "Hello");
    }

}

5. 消息监听

@Component
public class OrderMsgListener {

    @KafkaListener(topics = "order",groupId = "order-service")
    public void listen(ConsumerRecord record){
        System.out.println("收到消息："+record); //可以监听到发给kafka的新消息，以前的拿不到
    }

    @KafkaListener(groupId = "order-service-2",topicPartitions = {
            @TopicPartition(topic = "order",partitionOffsets = {
                    @PartitionOffset(partition = "0",initialOffset = "0")
            })
    })
    public void listenAll(ConsumerRecord record){
        System.out.println("收到partion-0消息："+record);
    }
}

6. 参数配置

消费者

spring.kafka.consumer.value-deserializer=org.springframework.kafka.support.serializer.JsonDeserializer
spring.kafka.consumer.properties[spring.json.value.default.type]=com.example.Invoice
spring.kafka.consumer.properties[spring.json.trusted.packages]=com.example.main,com.example.another

生产者

spring.kafka.producer.value-serializer=org.springframework.kafka.support.serializer.JsonSerializer
spring.kafka.producer.properties[spring.json.add.type.headers]=false