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夯实 kafka 系列|第五章：基于 kafka 分布式事件框架 eval-event

1.前言

本文分享基于 kafka 的分布式事件框架，从 0 到 1 的实现过程

• 从 需求->设计->开发->测试 一起来实现一个分布式事件框架；

• 使用方式类似于 Spring Event，事件可以在微服务集群中传递。

源码已上传 github

• https://github.com/huajiexiewenfeng/eval-event

2.需求

2.1 描述

1.事件机制在集群中传递

• 微服务发送事件消息
• 微服务订阅事件消息

2.事件通过kafka 来进行发送和监听

2.2 使用方式

2.2.1 事件 Event

每个自定义事件对应一个 kafka 中的 topic

• 继承 EvalEvent

• 重写 getTopic 方法

  • 设置事件存储的 topic 名称

public class MyEvent extends EvalEvent {private String message;...@Overridepublic String getTopic() {return "my-test-topic";}
}

2.2.2 服务端 Publisher

EvalEventPublisher.publishEvent 发送事件

@RestController
@RequestMapping(value = {"/api/eval/event/v1"})
public class HelloController {@Autowiredprivate EvalEventPublisher<MyEvent> evalEventPublisher;@RequestMapping("/hello")public String hello() {MyEvent myEvent = new MyEvent();myEvent.setMessage("Hello, World!");// 发送事件evalEventPublisher.publishEvent(myEvent);return "ok";}
}

2.2.3 客户端 Listener

• @EvalEventListener 注解方式（本文未实现该方式，有机会在下一篇文章中实现）

@EvalEventListener 
public void onEvalEvent(MyEvent event){...
}

• 实现 Listener 接口方式

@Component
public class TestEventListener implements EvalEventListener<MyEvent> {...@Overridepublic void onEvent(MyEvent event) {...}
}

3.设计

3.1 接口设计

3.1.1 事件监听者

public interface EvalEventListener<T extends EvalEvent> {/*** 事件处理方法** @param event 事件*/void onEvent(T event);
}

3.1.2 事件发送者

public interface EvalEventPublisher<T extends EvalEvent> {/*** 发送事件** @param event 事件*/void publishEvent(T event);
}

3.1.3 事件

public abstract class EvalEvent implements Serializable {private static final long serialVersionUID = 1L;/*** 事件ID 对应 Kafka message 的 key*/private String id = UUID.randomUUID().toString();public abstract String getTopic();public String getId() {return id;}public void setId(String id) {this.id = id;}
}

3.2 EvalEventPublisher kafka 实现

需要实现

• 初始化 kafka producer
• producer 发送 event

package com.csdn.event.kafka.publisher;import com.csdn.event.kafka.config.EvalKafkaProperties;
import com.csdn.event.sdk.EvalEvent;
import org.apache.kafka.clients.producer.KafkaProducer;
import org.apache.kafka.clients.producer.Producer;
import org.apache.kafka.clients.producer.ProducerConfig;
import org.apache.kafka.clients.producer.ProducerRecord;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;import javax.annotation.PostConstruct;
import java.util.Properties;@Component
public class KafkaEvalEventPublisher<T extends EvalEvent> implements EvalEventPublisher<T> {private static final Logger log = LoggerFactory.getLogger(KafkaEvalEventPublisher.class);@Autowiredprivate EvalKafkaProperties kafkaProperties;private Producer<String, EvalEvent> producer;@PostConstructpublic void init() {try {// Initialize the Kafka producerProperties props = new Properties();props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, kafkaProperties.getBootstrapServers());props.put(ProducerConfig.ACKS_CONFIG, kafkaProperties.getProducer().getAcks());props.put(ProducerConfig.RETRIES_CONFIG, kafkaProperties.getProducer().getRetries());props.put(ProducerConfig.BATCH_SIZE_CONFIG, kafkaProperties.getProducer().getBatchSize());props.put(ProducerConfig.LINGER_MS_CONFIG, kafkaProperties.getProducer().getLingerMs());props.put(ProducerConfig.BUFFER_MEMORY_CONFIG, kafkaProperties.getProducer().getBufferMemory());props.put(ProducerConfig.MAX_REQUEST_SIZE_CONFIG, kafkaProperties.getProducer().getMaxRequestSize());props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, "org.apache.kafka.common.serialization.StringSerializer");props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, "org.springframework.kafka.support.serializer.JsonSerializer");producer = new KafkaProducer<>(props);} catch (Exception e) {log.error(">>>> Kafka producer initialization failed", e);}}@Overridepublic void publishEvent(T event) {producer.send(buildRecord(event), (recordMetadata, e) -> {if (e != null) {log.error(String.format(">>>> 事件id:%s, topic:%s, 发送失败", event.getId(), event.getTopic()), e);} else {log.debug(">>>> 事件id:{}, topic:{}, 发送成功", event.getId(), event.getTopic());}});}private ProducerRecord<String, EvalEvent> buildRecord(EvalEvent t) {return new ProducerRecord<>(t.getTopic(), t.getId(), t);}}

3.3 EvalEventListener kafka 实现

3.3.1 KafkaEvalEventDispatcher 事件处理者

• 反射方式找到 EvalEvent 和 listener 的映射关系
• 循环 EvalEventListener
• 启动 EvalEventListenerThread 事件监听处理线程

@Component
@ConditionalOnProperty(value = "event.kafka.listener.enabled", havingValue = "true")
public class KafkaEvalEventDispatcher<T extends EvalEvent> {private static final Logger log = LoggerFactory.getLogger(KafkaEvalEventDispatcher.class);@Autowiredprivate List<EvalEventListener<T>> listeners;@Autowiredprivate EventKafkaConsumerFactory eventKafkaConsumerFactory;@Value("${event.kafka.base-package:com}")private String basePackage;@PostConstructpublic void init() {log.info(">>>> KafkaEvalEventListener initialized");// 反射方式找到 EvalEvent 和 listener 的映射关系try {Map<String, EvalEventDefinition> evalEventDefinitionsMap = EvalEventSubclassScannerUtil.getEvalEventDefinitions(basePackage);log.info(">>>> KafkaEvalEventListener topicMap: {}", evalEventDefinitionsMap);for (EvalEventListener<T> listener : listeners) {// 获取监听器的类名String cla = listener.getClass().getName();if (evalEventDefinitionsMap.containsKey(cla)) {EvalEventDefinition evalEventDefinition = evalEventDefinitionsMap.get(cla);log.info(">>>> KafkaEvalEventListener found listener: {}", evalEventDefinition);EvalEventListenerThread<T> evalEventListenerThread = new EvalEventListenerThread<>(evalEventDefinition, listener, eventKafkaConsumerFactory);evalEventListenerThread.start();}}} catch (Exception e) {e.printStackTrace();}}}

3.3.2 EvalEventListenerThread 事件监听线程

• 创建 KafkaConsumer
• Consumer 拉取消息 records
• 处理消息 records
• ack 提交

public class EvalEventListenerThread<T extends EvalEvent> extends Thread {...此处省略N行代码@Overridepublic void run() {// 1. 创建KafkaConsumerKafkaConsumer<String, ?> consumer;try {consumer = eventKafkaConsumerFactory.buildKafkaConsumer(evalEventListener);List<String> topicList = new ArrayList<>();topicList.add(evalEventDefinition.getTopic());consumer.subscribe(topicList);} catch (Exception e) {log.error("KafkaConsumer构造失败", e);e.printStackTrace();return;}// 2. 消费消息try {while (true) {try {// 3. 拉取消息ConsumerRecords<String, ?> records = consumer.poll(Duration.ofMillis(500));if (records.isEmpty()) {continue;}// 4. 处理消息dispatch(records);// 5. 使用异步提交规避阻塞consumer.commitAsync();} catch (Exception e) {log.error("消息处理异常", e);}}} finally {try {// 6.最后一次提交使用同步阻塞式提交consumer.commitSync();} finally {consumer.close();}}}...此处省略N行代码

3.3.3 其他细节

还有很多细节就不在这里赘述了，比如

• 序列化-自定义 Json 序列化
  • 这个需要自己来实现，因为默认提供的 json 序列化，会出现 Java Class 不匹配的情况
    • com.csdn.event.kafka.serialization.JsonDeserializer
    • com.csdn.event.kafka.serialization.JsonSerializer
• 反射获取 EventListener 泛型工具类
  • com.csdn.event.kafka.utils.EvalEventSubclassScannerUtil
• 提交优化
  • 同时使用了 commitSync() 和 commitAsync()。对于常规性、阶段性的手动提交，我们调用 commitAsync() 避免程序阻塞，而在 Consumer 要关闭前，我们调用 commitSync() 方法执行同步阻塞式的位移提交，以确保 Consumer 关闭前能够保存正确的位移数据

4.测试

4.1 发送事件测试

4.1.1 Hello World

@RestController
@RequestMapping(value = {"/api/eval/event/v1"})
public class HelloController {@Autowiredprivate EvalEventPublisher<MyEvent> evalEventPublisher;@GetMapping("/hello")public String hello() {MyEvent myEvent = new MyEvent();myEvent.setMessage("Hello, World!");// 发送事件evalEventPublisher.publishEvent(myEvent);return "ok";}
}

postman 发送请求

断点1

断点2

kafka tools 查看 topic 消息

4.1.2 发送 Bean 对象

HelloController 新增接口

    @Autowiredprivate EvalEventPublisher<UserCreatedEvent> userEventPublisher;  @GetMapping("/user")public String user() {UserCreatedEvent userCreatedEvent = new UserCreatedEvent();User user = new User("xwf", 18);userCreatedEvent.setUser(user);// 发送事件userEventPublisher.publishEvent(userCreatedEvent);return "ok";}

UserCreatedEvent 用户创建事件

public class UserCreatedEvent extends EvalEvent {private User user;public UserCreatedEvent() {}public UserCreatedEvent(User user) {this.user = user;}public User getUser() {return user;}public void setUser(User user) {this.user = user;}@Overridepublic String getTopic() {return "user-create-topic";}

测试结果
kafka 中的消息如下：

4.2 监听事件测试

4.2.1 源码调试

断点1

• listeners -》MyEventEventListener
• 同时获取到对应的 EvalEventDefinition
  • topic -》my-test-topic 用于 consumer 拉取 topic 消息
  • eventClass-》com.csdn.example.listener.model.MyEvent（自定事件）用于消息反序列化

断点2，EvalEventListenerThread 拉取 kafka 消息

最终调用方法

• UserEventEventListener#onEvent

4.2.2 监听 MyEvent 自定义事件

4.2.3 监听 UserCreatedEvent 自定义事件