事件发布订阅实现，我们经常使用到spring框架提供的ApplicationEventPublisher，基于kafka的特性，我们也可以简单实现类似的效果

1、kafka环境部署搭建

官网下载链接：https://kafka.apache.org/downloads，最开始用最新版的，发现在我的win10系统没部署成功，所以还是选择2.8.1版本的

在D:\kafka_2.12-2.8.1\bin\windows，使用cmd命令启动zookeeper，window系统修改conf文件夹下面的zookeeper.properties里面的dataDir

zookeeper-server-start.bat ..\..\config\zookeeper.properties

window系统修改conf文件夹下面的log.dirs路径

kafka-server-start.bat ..\..\config\server.properties

2、kafka常用命令使用

启动另外一个cmd参考，创建一个命令为test-topic的topic

kafka-topics.bat --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic test-topic

查看kafkatopic列表

kafka-topics.bat --list --zookeeper localhost:2181

启动kafka的生产者，发送topic数据

kafka-console-producer.bat --broker-list localhost:9092 --topic test-topic

启动一个kafka消费者端，可以接收到消息数据

kafka-console-consumer.bat --bootstrap-server localhost:9092 --topic test-topic --from-beginning

3、创建一个kafka starter工程

创建一个工程，实现对kafka的api简单封装

jdk选择jdk8的

选择需要的依赖

基于kafka的EventPublisher

package com.example.ebus.publisher;

import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.ApplicationEvent;
import org.springframework.kafka.core.KafkaTemplate;

@Slf4j
public class MyEventPublisher {

    private KafkaTemplate<String, Object> kafkaTemplate;

    @Value("${app.ebus.topic:ebus}")
    private String topic;

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

    public void publishEvent(Object event) {
        if (log.isInfoEnabled()) {
            log.info("topic发送:{}", event.getClass().getName());
        }
        kafkaTemplate.send(topic, event);
    }

}

自动配置类

package com.example.ebus.configuration;

import com.example.ebus.publisher.MyEventPublisher;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.kafka.core.KafkaTemplate;

@Configuration
public class EbusAutoConfiguration {

    @Bean
    public MyEventPublisher myEventPublisher(@Qualifier("kafkaTemplate") KafkaTemplate<String, Object> kafkaTemplate) {
        return new MyEventPublisher(kafkaTemplate);
    }

}

META-INF/spring.factories，加上配置

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.example.ebus.configuration.EbusAutoConfiguration

4、kafka生产端实现

同样创建一个生产者端工程，引入starter，加上yml配置

spring:
  kafka:
    bootstrap-servers: 127.0.0.1:9092
    producer:
      value-serializer: org.springframework.kafka.support.serializer.JsonSerializer

写个测试接口测试数据：

package com.example.producer.controller;

import com.example.ebus.event.ShopOrderEvent;
import com.example.ebus.publisher.MyEventPublisher;
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.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping(value = "/api")
public class ShopOrderController {

    @Autowired
    private MyEventPublisher eventPublisher;

    @PostMapping("/order")
    public String placeOrder(@RequestBody ShopOrderEvent orderEvent) {
        eventPublisher.publishEvent(orderEvent);
        return orderEvent.getOrderCode();
    }
}

{
    "orderCode":"123456",
    "productName":"三星手机",
    "price":1122,
    "productDesc":"三星手机"
}

5、kafka消费者端实现

同样创建一个消费者工程

spring:
  kafka:
    bootstrap-servers: 127.0.0.1:9092
    consumer:
      enable-auto-commit: true
      group-id: consumer1
      value-deserializer: org.springframework.kafka.support.serializer.JsonDeserializer
      max-poll-records: 1
      properties:
        spring:
          json:
            trusted:
              packages: '*'

进行监听，使用kafka的KafkaListener

package com.example.consumer.handler;

import com.example.ebus.event.ShopOrderEvent;
import lombok.extern.slf4j.Slf4j;
import org.springframework.kafka.annotation.KafkaListener;
import org.springframework.stereotype.Component;

@Component
@Slf4j
public class OrderListenerHandler {

    @KafkaListener(topics = {"${app.ebus.topic:ebus}"})
    public void obtainTopicData(ShopOrderEvent event) {
        log.info("下单成功,orderCode:{}" , event.getOrderCode());
    }

}

本博客代码例子可以在GitHub找到下载链接

参考资料

• https://kafka.apache.org/documentation/
• https://blog.csdn.net/qq_36391986/article/details/88364538
• https://blog.csdn.net/qq_26803795/article/details/105682276