Question

我找到了一个关于spring-kafka的教程，他们在那里创建了一个生产者和消费者。但是，该程序是通过测试用例运行的。随着测试用例的结束，消费者停止了。

如何确保消费者继续在backgorund中运行，以便我可以从终端命令行测试一些消息。

SpringKafkaExampleApplication.java

package com.howtoprogram.kafka;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SpringKafkaExampleApplication {
    public static void main(String[] args) {
        SpringApplication.run(SpringKafkaExampleApplication.class, 
        args);
    }
}

KafkaProducerConfig.java

package com.howtoprogram.kafka;

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

import org.apache.kafka.clients.producer.ProducerConfig;
import org.apache.kafka.common.serialization.StringSerializer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.kafka.annotation.EnableKafka;
import org.springframework.kafka.core.DefaultKafkaProducerFactory;
import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.kafka.core.ProducerFactory;

@Configuration
@EnableKafka
public class KafkaProducerConfig {
    @Bean
    public ProducerFactory<String, String> producerFactory() {
        return new DefaultKafkaProducerFactory<>(producerConfigs());
    }

    @Bean
    public Map<String, Object> producerConfigs() {
        Map<String, Object> props = new HashMap<>();
        props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, 
        "localhost:9092");
        props.put(ProducerConfig.RETRIES_CONFIG, 0);
        props.put(ProducerConfig.BATCH_SIZE_CONFIG, 16384);
        props.put(ProducerConfig.LINGER_MS_CONFIG, 1);
        props.put(ProducerConfig.BUFFER_MEMORY_CONFIG, 33554432);
        props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, 
        StringSerializer.class);
        props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, 
        StringSerializer.class);
        return props;
    }

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

KafkaConsumerConfig.java

package com.howtoprogram.kafka;

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

import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.common.serialization.StringDeserializer;
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.config.KafkaListenerContainerFactory;
import org.springframework.kafka.core.ConsumerFactory;
import org.springframework.kafka.core.DefaultKafkaConsumerFactory;
import org.springframework.kafka.listener.ConcurrentMessageListenerContainer;

@Configuration
@EnableKafka
public class KafkaConsumerConfig {
    @Bean
    KafkaListenerContainerFactory<ConcurrentMessageListenerContainer<String, String>> kafkaListenerContainerFactory() {
        ConcurrentKafkaListenerContainerFactory<String, String> factory = new ConcurrentKafkaListenerContainerFactory<>();
        factory.setConsumerFactory(consumerFactory());
        factory.setConcurrency(3);
        factory.getContainerProperties().setPollTimeout(3000);
        return factory;
    }

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

    @Bean
    public Map<String, Object> consumerConfigs() {
        Map<String, Object> propsMap = new HashMap<>();
        propsMap.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
        propsMap.put(ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG, false);
        propsMap.put(ConsumerConfig.AUTO_COMMIT_INTERVAL_MS_CONFIG, "100");
        propsMap.put(ConsumerConfig.SESSION_TIMEOUT_MS_CONFIG, "15000");
        propsMap.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
        propsMap.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
        propsMap.put(ConsumerConfig.GROUP_ID_CONFIG, "group1");
        propsMap.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");
        return propsMap;
    }

    @Bean
    public Listener listener() {
        return new Listener();
    }
}

Listener.java

package com.howtoprogram.kafka;

import java.util.concurrent.CountDownLatch;

import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.springframework.kafka.annotation.KafkaListener;

public class Listener {

public final CountDownLatch countDownLatch1 = new CountDownLatch(1);

    @KafkaListener(id = "foo", topics = "topic1", group = "group1")
    public void listen(ConsumerRecord<?, ?> record) {
        System.out.println(record);
        countDownLatch1.countDown();
    }

}

SpringKafkaExampleApplicationTests.java

package com.howtoprogram.kafka;

import static org.assertj.core.api.Assertions.assertThat;

import java.util.concurrent.TimeUnit;

import org.junit.ClassRule;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.kafka.support.SendResult;
import org.springframework.kafka.test.rule.KafkaEmbedded;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.util.concurrent.ListenableFuture;
import org.springframework.util.concurrent.ListenableFutureCallback;

@RunWith(SpringRunner.class)
@SpringBootTest
public class SpringKafkaExampleApplicationTests {

@Autowired
private KafkaTemplate<String, String> kafkaTemplate;
@Autowired
private Listener listener;

@Test
public void contextLoads() throws InterruptedException {

    ListenableFuture<SendResult<String, String>> future = kafkaTemplate.send("topic1", "ABC");
    future.addCallback(new ListenableFutureCallback<SendResult<String, String>>() {
        @Override
        public void onSuccess(SendResult<String, String> result) {
            System.out.println("success");
        }

        @Override
        public void onFailure(Throwable ex) {
            System.out.println("failed");
        }
    });
    System.out.println(Thread.currentThread().getId());
    assertThat(this.listener.countDownLatch1.await(60, TimeUnit.SECONDS)).isTrue();

}

}

请帮忙！

Answer 1

在main之后将此代码添加到SpringApplication.run()：

System.out.println("Hit 'Enter' to terminate");
System.in.read();
ctx.close();
System.exit(0);

您的程序不会退出，直到您按下控制台中的Enter按钮。

Answer 2

我们在一个while(true)循环中运行我们的Kafka应用程序，并在Spring Bean上使用@Scheduled：https://docs.spring.io/spring/docs/current/spring-framework-reference/html/scheduling.html 这样，您还可以在应用程序的其余部分初始化时延迟消息的消耗。

@Scheduled(initialDelay = 5000L, fixedDelay = 10000L)
public void process() {

  while (keepRunning) {
    try {
      ConsumerRecords<String, String> records = consumer.poll(500);
      // do processing here
    }
  }
}

fixedDelay有点奇怪。该值必须可用，但实际上会被忽略。

在@PostConstruct中启动使用者可能很诱人但是这样Spring一直认为bean处于初始阶段。（所以不要像Artem Bilan在下面提到的那样这样做）

spring-kafka如何在后台运行消费者

2 个答案: