Co to jest Spring AMQP i RabbitMQ?

@Configuration
public class HelloWorldConfiguration {

    protected final String helloWorldQueueName = "hello.world.queue";

    @Bean
    public ConnectionFactory connectionFactory() {
        CachingConnectionFactory connectionFactory = new CachingConnectionFactory("localhost");
        connectionFactory.setUsername("guest");
        connectionFactory.setPassword("guest");
        return connectionFactory;
    }

    @Bean
    public AmqpAdmin amqpAdmin() {
        return new RabbitAdmin(connectionFactory());
    }

    @Bean
    public RabbitTemplate rabbitTemplate() {
        RabbitTemplate template = new RabbitTemplate(connectionFactory());
        // Klucz routingu jest ustawiony na nazwę kolejki
        template.setRoutingKey(this.helloWorldQueueName);
        // Miejsce, z którego będziemy odbierać wiadomości
        template.setDefaultReceiveQueue(this.helloWorldQueueName);
        return template;
    }

    @Bean
    // Tworzymy nową beana nowej kolejki
    public Queue helloWorldQueue() {
        return new Queue(this.helloWorldQueueName);
    }
}

@Configuration
public class ConsumerConfiguration extends HelloWorldConfiguration {

    @Bean
    public SimpleMessageListenerContainer listenerContainer() {
        SimpleMessageListenerContainer container = new SimpleMessageListenerContainer();
        container.setConnectionFactory(connectionFactory());
        container.setQueueNames(this.helloWorldQueueName);
        container.setMessageListener(new MessageListenerAdapter(new HelloWorldHandler()));
        return container;
    }
}

@Configuration
public class ProducerConfiguration {

    protected final String helloWorldQueueName = "hello.world.queue";

    @Bean
    public RabbitTemplate rabbitTemplate() {
        RabbitTemplate template = new RabbitTemplate(connectionFactory());
        template.setRoutingKey(this.helloWorldQueueName);
        return template;
    }

    @Bean
    public ConnectionFactory connectionFactory() {
        CachingConnectionFactory connectionFactory = new CachingConnectionFactory("localhost");
        connectionFactory.setUsername("guest");
        connectionFactory.setPassword("guest");
        return connectionFactory;
    }

    @Bean
    public ScheduledProducer scheduledProducer() {
        return new ScheduledProducer();
    }

    @Bean
    public BeanPostProcessor postProcessor() {
        return new ScheduledAnnotationBeanPostProcessor();
    }


    static class ScheduledProducer {

        @Autowired
        private volatile RabbitTemplate rabbitTemplate;

        private final AtomicInteger counter = new AtomicInteger();

        @Scheduled(fixedRate = 3000)
        public void sendMessage() {
            rabbitTemplate.convertAndSend("Hello World " + counter.incrementAndGet());
        }
    }
}

rabbitTemplate.convertAndSend("myQueue", "Hello, world!");

@RabbitListener(queues = "myQueue")
public void listen(String in) {
    System.out.println("Message read from myQueue : " + in);
}

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-amqp</artifactId>
        <version>X.Y.Z.RELEASE</version>
    </dependency>
</dependencies>