请编写代码实现一个Spring Cloud Bus的案例 ？

Spring Cloud Bus是一个用于在集群中传播消息的轻量级消息代理，通常与Spring Cloud Config一起使用，以实现配置更改的广播。以下是一个简单的Spring Cloud Bus案例，包括两个服务，它们通过Spring Cloud Bus通信以广播消息。

1. 首先，在父POM中，我们需要包含Spring Cloud和Spring Boot的依赖。

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.5.4</version>
    <relativePath/> <!-- lookup parent from repository -->
</parent>

<properties>
    <java.version>1.8</java.version>
    <spring-cloud.version>2020.0.1</spring-cloud.version>
</properties>

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-dependencies</artifactId>
            <version>${spring-cloud.version}</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

<dependencies>
    <!-- other dependencies -->
</dependencies>

2. 创建第一个服务service-bus-sender，用于发送消息。

application.yml

spring:
  application:
    name: service-bus-sender
  cloud:
    bus:
      trace:
        enabled: true
    stream:
      kafka:
        binder:
          brokers: localhost:9092
      bindings:
        output:
          destination: topic.bus

SenderApplication.java

@SpringBootApplication
public class SenderApplication {

    @Autowired
    private StreamBridge streamBridge;

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

    @Scheduled(fixedRate = 5000)
    public void sendMessage() {
        streamBridge.send("output", MessageBuilder.withPayload("Hello from service-bus-sender at " + LocalDateTime.now()).build());
    }
}

3. 创建第二个服务service-bus-receiver，用于接收消息。

application.yml

spring:
  application:
    name: service-bus-receiver
  cloud:
    bus:
      trace:
        enabled: true
    stream:
      kafka:
        binder:
          brokers: localhost:9092
      bindings:
        input:
          destination: topic.bus
          group: bus-receiver

ReceiverController.java

@RestController
public class ReceiverController {

    @Autowired
    private StreamListener streamListener;

    @GetMapping("/receive")
    public String receiveMessage() {
        return streamListener.getLastReceivedMessage();
    }
}

StreamListener.java

@Component
public class StreamListener {

    private String lastReceivedMessage;

    @StreamListener(target = "input")
    public void handle(String message) {
        this.lastReceivedMessage = message;
    }

    public String getLastReceivedMessage() {
        return lastReceivedMessage;
    }
}

4. 启动两个服务，并访问service-bus-receiver的/receive端点，你应该可以看到从service-bus-sender发送过来的消息。

请注意，为了简单起见，此示例使用了Kafka作为消息代理。在实际生产环境中，你可能需要使用RabbitMQ、ActiveMQ等其他消息代理。此外，你还需要确保已经正确配置了Kafka或所选的消息代理。