Implementing Spring Boot messaging

In an ideal case, all microservice interactions are expected to happen asynchronously using publish-subscribe semantics. Spring Boot provides a hassle-free mechanism to configure messaging solutions:

Implementing Spring Boot messaging

In this example, we will create a Spring Boot application with a sender and receiver, both connected though an external queue. Perform the following steps:

Note

The full source code of this example is available as the chapter2.bootmessaging project in the code files of this book.

  1. Create a new project using STS to demonstrate this capability. In this example, instead of selecting Web, select AMQP under I/O:
    Implementing Spring Boot messaging
  2. Rabbit MQ will also be needed for this example. Download and install the latest version of Rabbit MQ from https://www.rabbitmq.com/download.html.

    Rabbit MQ 3.5.6 is used in this book.

  3. Follow the installation steps documented on the site. Once ready, start the RabbitMQ server via the following command:
    $./rabbitmq-server
  4. Make the configuration changes to the application.properties file to reflect the RabbitMQ configuration. The following configuration uses the default port, username, and password of RabbitMQ:
    spring.rabbitmq.host=localhost
spring.rabbitmq.port=5672
spring.rabbitmq.username=guest
spring.rabbitmq.password=guest
  5. Add a message sender component and a queue named TestQ of the org.springframework.amqp.core.Queue type to the Application.java file under src/main/java. RabbitMessagingTemplate is a convenient way to send messages, which will abstract all the messaging semantics. Spring Boot provides all boilerplate configurations to send messages:
    @Component 
class Sender {
  @Autowired
  RabbitMessagingTemplate template;
  @Bean
  Queue queue() {
    return new Queue("TestQ", false);
  }
  public void send(String message){
    template.convertAndSend("TestQ", message);
  }
}
  6. To receive the message, all that needs to be used is a @RabbitListener annotation. Spring Boot autoconfigures all the required boilerplate configurations:
    @Component
class Receiver {
    @RabbitListener(queues = "TestQ")
    public void processMessage(String content) {
       System.out.println(content);
    }
}
  7. The last piece of this exercise is to wire the sender to our main application and implement the run method of CommandLineRunner to initiate the message sending. When the application is initialized, it invokes the run method of CommandLineRunner, as follows:
    @SpringBootApplication
public class Application implements CommandLineRunner{

  @Autowired
  Sender sender;
  
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
    
    @Override
    public void run(String... args) throws Exception {
      sender.send("Hello Messaging..!!!");
    }
}
  8. Run the application as a Spring Boot application and verify the output. The following message will be printed in the console:
    Hello Messaging..!!!
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