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RabbitMQ Messaging & Async Systems · Aula

Exchange Direct para roteamento

Aprenda a usar a exchange Direct para roteamento preciso de mensagens com base em uma chave de roteamento. Direcione mensagens para filas específicas para um processamento direcionado.

Exchange Direct para roteamento é uma aula grátis de RabbitMQ Messaging & Async Systems no CoddyKit. Esta é a aula 2 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de RabbitMQ Messaging & Async Systems, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de RabbitMQ Messaging & Async Systems inclui 4 aulas no total.

Partes desta aula ainda não foram traduzidas e aparecem em inglês.

Introduction to Direct Exchange

Welcome! In this lesson, we'll explore the Direct Exchange in RabbitMQ. It's a powerful tool for sending messages to specific queues based on a routing key.

Think of it like a postal service that delivers letters only to the exact address specified on the envelope.

What is a Routing Key?

A routing key is a string attribute that producers attach to messages. It's essentially an "address" for the message.

  • Producers specify a routing key when publishing.
  • Queues bind to an exchange with one or more routing keys.
  • Messages are delivered to queues whose binding key exactly matches the message's routing key.

How Direct Exchange Works

When a message arrives at a Direct Exchange, it looks at the message's routing key. The exchange then delivers the message to all queues that are bound to it with an identical routing key.

If no queue is bound with that specific routing key, the message is simply discarded by the exchange.

Producer's Role: Sending with Keys

As a producer, you decide the routing key for each message you send. This key determines which consumer (via its bound queue) will receive the message.

This allows for precise control over message delivery, ensuring only relevant consumers get specific types of messages.

Consumer's Role: Binding with Keys

Consumers define their interest in messages by binding their queues to a Direct Exchange using specific routing keys.

A single queue can be bound with multiple routing keys, allowing it to receive messages matching any of those keys.

Code: Producer Setup & Declare

Let's set up a basic producer that uses a Direct Exchange. We'll declare an exchange named "direct_logs" with type "direct".

This code establishes a connection and channel, then declares the exchange.

import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;

public class DirectProducerSetup {
    private static final String EXCHANGE_NAME = "direct_logs";

    public static void main(String[] argv) throws Exception {
        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost"); // Assuming RabbitMQ is local

        try (Connection connection = factory.newConnection();
             Channel channel = connection.createChannel()) {

            channel.exchangeDeclare(EXCHANGE_NAME, "direct");
            System.out.println("Exchange '" + EXCHANGE_NAME + "' declared.");

            // In a real app, you'd send messages here
            // For this setup example, we just declare.
        }
    }
}

Code: Producer Sending Message

Now, let's send a message to our "direct_logs" exchange. We'll specify a routing key, for example, "error".

Run this code after ensuring your RabbitMQ server is running. It will publish a message with the specified key.

import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import java.nio.charset.StandardCharsets;

public class DirectProducerSend {
    private static final String EXCHANGE_NAME = "direct_logs";

    public static void main(String[] argv) throws Exception {
        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost"); // Assuming RabbitMQ is local

        try (Connection connection = factory.newConnection();
             Channel channel = connection.createChannel()) {

            channel.exchangeDeclare(EXCHANGE_NAME, "direct"); // Ensure exchange exists

            String routingKey = "error";
            String message = "A critical error occurred!";

            channel.basicPublish(EXCHANGE_NAME, routingKey, null, message.getBytes(StandardCharsets.UTF_8));
            System.out.println(" [x] Sent '" + routingKey + ":'" + message + "'");
        }
    }
}

Code: Consumer Setup & Binding

On the consumer side, we'll create a queue and bind it to the "direct_logs" exchange using the routing key "error".

This consumer will only receive messages published with the "error" routing key. Run this consumer first, then the producer.

import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.DeliverCallback;

public class DirectConsumerError {
    private static final String EXCHANGE_NAME = "direct_logs";

    public static void main(String[] argv) throws Exception {
        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost"); // Assuming RabbitMQ is local

        Connection connection = factory.newConnection();
        Channel channel = connection.createChannel();

        channel.exchangeDeclare(EXCHANGE_NAME, "direct");

        String queueName = channel.queueDeclare().getQueue(); // Create a non-durable, exclusive, auto-delete queue
        String bindingKey = "error";
        channel.queueBind(queueName, EXCHANGE_NAME, bindingKey);

        System.out.println(" [*] Waiting for messages with routing key '" + bindingKey + "'. To exit press CTRL+C");

        DeliverCallback deliverCallback = (consumerTag, delivery) -> {
            String message = new String(delivery.getBody(), "UTF-8");
            System.out.println(" [x] Received '" + delivery.getEnvelope().getRoutingKey() + ":'" + message + "'");
        };
        channel.basicConsume(queueName, true, deliverCallback, consumerTag -> {});
    }
}

Multiple Bindings & Use Cases

A single queue can bind to the same Direct Exchange with multiple routing keys. For instance, a "critical alerts" queue might bind to both "error" and "warning" keys to receive both types of messages.

Direct exchanges are perfect for scenarios like:

  • Distributing logs based on severity (e.g., info, warn, error).
  • Routing internal system events to specific processing modules.
  • Targeting updates to particular user segments.

Quick Check: Direct Routing

Consider a Direct Exchange named "my_exchange".

  • Queue A is bound with routing key "report".
  • Queue B is bound with routing key "alert".
  • Queue C is bound with routing keys "report" and "update".

A producer sends a message to "my_exchange" with the routing key "report".

Recap: Direct Exchange

Great job! You've learned about the Direct Exchange in RabbitMQ.

  • It routes messages based on an exact match of the routing key.
  • Producers attach a routing key to each message.
  • Consumers bind their queues to the exchange with specific routing keys to receive relevant messages.
  • This pattern allows for precise, targeted message delivery.

Next, we'll explore the Fanout Exchange, which broadcasts messages to all bound queues, regardless of routing key!

Perguntas Frequentes

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O que vou aprender em “Exchange Direct para roteamento”?

Aprenda a usar a exchange Direct para roteamento preciso de mensagens com base em uma chave de roteamento. Direcione mensagens para filas específicas para um processamento direcionado. Você pratica RabbitMQ Messaging & Async Systems com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.

Preciso ter experiência prévia para começar RabbitMQ Messaging & Async Systems?

Nenhuma experiência prévia é necessária. RabbitMQ Messaging & Async Systems no CoddyKit é estruturado para alunos iniciantes até avançados, então você pode começar aqui ou desde o início e aprender no seu ritmo. Esta é a aula 2 de 4.

Quanto tempo leva a aula “Exchange Direct para roteamento”?

A maioria das aulas CoddyKit leva cerca de 5–10 minutos. Cada uma é compacta e interativa, então você faz progresso constante e retoma exatamente de onde parou entre web e app.

Posso escrever e executar código nesta aula de RabbitMQ Messaging & Async Systems?

Sim. Cada aula de RabbitMQ Messaging & Async Systems inclui um editor de código integrado, então você escreve e executa código real direto no navegador e recebe feedback de IA instantaneamente — nenhuma configuração local necessária.

Todas as aulas deste curso

  1. Exchange Fanout para publicação e assinatura
  2. Exchange Direct para roteamento
  3. Exchange Topic para roteamento flexível
  4. Exchange padrão e vinculações implícitas
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