使用微服务Spring Cloud集成Kafka实现异步通信（消费者）

1、本文架构

本文目标是使用微服务Spring Cloud集成Kafka实现异步通信。其中Kafka Server部署在Ubuntu虚拟机上，微服务部署在Windows 11系统上，Kafka Producer微服务和Kafka Consumer微服务分别注册到Eureka注册中心。Kafka Producer和Kafka Consumer之间通过Kafka Server实现异步通信。

出于便于测试的目的，我通过浏览器触发Kafka Producer发送消息，观察Kafka Consumer的后台是否打印出接收到的消息内容。

Ubuntu 上部署Kafka Server，详见博文：Ubuntu下Kafka安装及使用-CSDN博客

Eureka注册中心的搭建过程和完整代码，详见博文：微服务1：搭建微服务注册中心（命令行简易版，不使用IDE）-CSDN博客

Kafka Producer微服务的完整代码，详见博文：使用微服务Spring Cloud集成Kafka实现异步通信-CSDN博客

本文的重点是实现下图中的深蓝色部分：Kafka Consumer微服务。

2、创建Spring boot项目（Kafka Consumer微服务项目）：

mvn archetype:generate -DgroupId=com.test -DartifactId=microservice-kafka-consumer -DarchetypeArtifactId=maven-archetype-quickstart

项目代码的完整目录如下图所示：

编辑pom.xml，添加依赖包：

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

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  
  <groupId>com.test</groupId>
  <artifactId>microservice-kafka-consumer</artifactId>
  <packaging>jar</packaging>
  <version>1.0-SNAPSHOT</version>
  <name>microservice-kafka-consumer</name>
  <url>http://maven.apache.org</url>
  
  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.3.0.RELEASE</version>
    <relativePath/> 
  </parent>
  
  <dependencies>
  	<dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
    </dependency>         
	 
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
    
    <dependency>
      <groupId>org.springframework.cloud</groupId>
      <artifactId>spring-cloud-stream-binder-kafka</artifactId>
    </dependency>


  </dependencies>
  
    <dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-dependencies</artifactId>
            <version>Hoxton.SR4</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>               
    </dependencies>
  </dependencyManagement>
  
  <build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>
  
</project>

编辑application.yml，配置kafka消费者：

consumer:
      #消费的主题
      topic: test-topic
      #消费者组id
      group-id: test-group
      #是否自动提交偏移量
      enable-auto-commit: true
      #提交偏移量的间隔-毫秒
      auto-commit-ms: 1000
      #客户端消费的会话超时时间-毫秒
      session-timeout-ms: 10000
      #实现DeSerializer接口的反序列化类键
      key-deserializer: org.apache.kafka.common.serialization.StringDeserializer
      #实现DeSerializer接口的反序列化类值
      value-deserializer: org.apache.kafka.common.serialization.StringDeserializer

server:
  port: 8030
spring:
  application:
    name: microservice-kafka-consumer
  kafka:
    bootstrap-servers: 192.168.23.131:9092
    consumer:
      group-id: test-group
      enable-auto-commit: true
      auto-commit-ms: 1000
      session-timeout-ms: 10000
      key-deserializer: org.apache.kafka.common.serialization.StringDeserializer
      value-deserializer: org.apache.kafka.common.serialization.StringDeserializer

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8080/eureka/
  instance:
    prefer-ip-address: true            

App.java的完整代码如下：

package com.test;

import org.springframework.boot.ApplicationRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.kafka.annotation.KafkaListener;


@SpringBootApplication
@EnableDiscoveryClient
public class App 
{
	
	  @KafkaListener(topics = "mydemo1")
    public void listen(String msg) throws Exception {
        System.out.println( "-----> Recv a msg: " + msg );
    }
    
    public static void main( String[] args ){
        System.out.println( "Hello World!" );
        SpringApplication.run(App.class, args);
    }
}

3、测试

在浏览器输入，触发Kafka Producer向Kafka Server发送消息：

http://localhost:8020/kafka/sendMsg?msg=测试消息testmsg

在Kafka Consumer的后台打印出收到的消息：