How send reply from listener

Question

I am working on homework to my studies with Java and RabbitMQ. I am not familiar much with Spring and RabbitMQ, but I can't handle this problem.

I have 2 single application.

First one, which produces the message (bolid application) I created a producer of the message (bolid), which every 10 seconds send a message to listeners

@SpringBootApplication
public class BolidApplication implements CommandLineRunner {

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

    @Autowired
    private RabbitTemplate rabbitTemplate;

    @Override
    public void run(String... args) throws Exception {

        Bolid bolid = new Bolid();
        int i = 10;
        while (true) {
            bolid.setData(new Date());
            rabbitTemplate.setReplyAddress("bolidReply");
            rabbitTemplate.convertAndSend("RaceExchange", "raceRouting", bolid.toString());
            rabbitTemplate.convertAndSend("MonitorExchange", "raceRouting", bolid.toString());
            Thread.sleep(15000);
            i += 10;
        }
    }
}

So, I create 2 queue (RaceQueue and MonitorQueue), define exchange and bind them.

I have 2 listeners: RaceListener and MonitorListener.

There is the code of my listeners:

And the second application, which is listeners.

public class RabbitConfig {
    private static final String RACE_QUEUE = "RaceQueue";
    private static final String MONITOR_QUEUE = "MonitorQueue";

    @Bean
    Queue myQueue() {
        return new Queue(RACE_QUEUE, true);
    }

    @Bean
    Queue monitorQueue() {
        return new Queue(MONITOR_QUEUE, true);
    }

    @Bean
    Exchange myExchange() { 
        return ExchangeBuilder.topicExchange("RaceExchange")
                .durable(true)
                .build();
    }

    @Bean
    Exchange monitorExchange() { 
        return ExchangeBuilder.topicExchange("MonitorExchange")
                .durable(true)
                .build();
    }

    @Bean
    Binding binding() {
//        return new Binding(MY_QUEUE, Binding.DestinationType.QUEUE, "MyTopicExchange", "topic", null)
        return BindingBuilder
                .bind(myQueue())
                .to(myExchange())
                .with("raceRouting")
                .noargs();
    }

    @Bean
    Binding monitorBinding() {
        return BindingBuilder
                .bind(monitorQueue())
                .to(monitorExchange())
                .with("raceRouting")
                .noargs();
    }

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

    @Bean
    MessageListenerContainer rabbitRaceListener() {
        SimpleMessageListenerContainer simpleMessageListenerContainer = new SimpleMessageListenerContainer();
        simpleMessageListenerContainer.setConnectionFactory(connectionFactory());
        simpleMessageListenerContainer.setQueues(myQueue());
        simpleMessageListenerContainer.setupMessageListener(new RabbitRaceListener());
        return simpleMessageListenerContainer;
    }

    @Bean
    MessageListenerContainer rabbitMonitorListener() {

        SimpleMessageListenerContainer simpleMessageListenerContainer = new SimpleMessageListenerContainer();
        simpleMessageListenerContainer.setConnectionFactory(connectionFactory());
        simpleMessageListenerContainer.setQueues(monitorQueue());
        simpleMessageListenerContainer.setupMessageListener(new RabbitMonitorListener());
        return simpleMessageListenerContainer;
    }
}

From MonitorListener I want to use reply pattern to reply message to my first application (bolid application). So Bolid application can receive my message.

My Code for MonitorListener:

public class RabbitMonitorListener implements MessageListener {
    @Autowired
    private RabbitTemplate rabbitTemplate;
    @Override
    public void onMessage(Message message) {
        String[] splitted = new String(message.getBody()).split("\\|");
        int oilTemperature = Integer.parseInt(splitted[1].split(" ")[2]);
        int engineTemperature = Integer.parseInt(splitted[2].split(" ")[2]);
        int tirePressure = Integer.parseInt(splitted[3].split(" ")[2]);

        System.out.println("message2 = [" + new String(message.getBody()) + "]");

        if (oilTemperature > 120 || engineTemperature > 120 || tirePressure > 12) {
            System.out.println("SEND REPLY TO BOLID!");
        }
        if (oilTemperature > 150 || engineTemperature > 150 || tirePressure > 17) {
            System.out.println("SEND RELY TO BOLID!");
        }
    }
}

How can I achieve that? So here I can send the message go back to bolid and on the bolid application I can read it?

EDIT: I did some research, I want to do it like this way:

public class RabbitMonitorListener implements MessageListener {
    @Autowired
    private RabbitTemplate rabbitTemplate;

    @Override
    public void onMessage(Message message) {
        String[] splitted = new String(message.getBody()).split("\\|");
        int oilTemperature = Integer.parseInt(splitted[1].split(" ")[2]);
        int engineTemperature = Integer.parseInt(splitted[2].split(" ")[2]);
        int tirePressure = Integer.parseInt(splitted[3].split(" ")[2]);
        String response = "Hello";
        MessageProperties properties = new MessageProperties();
        Message responseMessage = new Message(response.getBytes(), properties);
        rabbitTemplate.send(message.getMessageProperties().getReplyTo(), responseMessage);

        System.out.println("message2 = [" + new String(message.getBody()) + "]");

        if (oilTemperature > 120 || engineTemperature > 120 || tirePressure > 12) {
            System.out.println("WARN MECHANICS");

        }
        if (oilTemperature > 150 || engineTemperature > 150 || tirePressure > 17) {
            System.out.println("WARN MECHANICS");
        }
    }
}

but the rabbitTemplate is null here, so I can't @Autowired it here. How can I have access to rabbitTemplate and method send in MessageListener?

Gary Russell · Accepted Answer · 2019-04-27 15:15:01Z

2

new RabbitRaceListener() - that must be a @Bean too, to get auto wiring.

However, you are over-complicating things; the framework can take care of all of this for you.

See Request/Reply Messaging for the client side - and use convertSendAndReceive() or convertSendAndReceiveAsType().

On the server side, see Annotation-driven Listener Endpoints.

@RabbitListener(queues = "request")
public String handle(String in) {
    return in.toUpperCase();
}

answered Apr 27, 2019 at 15:15

Gary Russell

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