Exchange Topic per un routing flessibile
Padroneggi l'exchange Topic per gestire pattern di routing complessi tramite il wildcard matching. Progetti topologie di routing dei messaggi flessibili e scalabili.
Exchange Topic per un routing flessibile è una lezione RabbitMQ Messaging & Async Systems gratuita su CoddyKit. Questa è la lezione 3 di 4. Puoi leggere la lezione completa qui gratuitamente — poi esercitati direttamente nel browser con un editor di codice integrato e un tutor IA disponibile 24/7. Fa parte del percorso di apprendimento RabbitMQ Messaging & Async Systems, e i tuoi progressi si sincronizzano tra il web e l'app CoddyKit. Il corso RabbitMQ Messaging & Async Systems include 4 lezioni in totale.
Parti di questa lezione non sono ancora state tradotte e vengono mostrate in inglese.
Topic Exchange: Flexible Routing
Welcome to the Topic Exchange! This exchange type offers the most flexible message routing, letting you send messages to queues based on complex patterns.
Unlike the simple Fanout or direct-match Direct exchange, Topic exchanges use special wildcards in routing keys to match messages dynamically.
Understanding Topic Routing Keys
With a Topic exchange, routing keys aren't exact matches. They are strings made of words separated by dots (.), much like parts of a filename or URL.
- Example:
animal.rabbit.fast - Example:
log.error.database
Each word provides a level of detail, allowing for hierarchical routing.
The Single-Word Wildcard: `*`
The asterisk (*) wildcard matches exactly one word in a routing key segment.
- Binding key:
animal.*.fastmatchesanimal.rabbit.fast - Binding key:
animal.*.fastdoes not matchanimal.dog.lazy.fast(too many words) - Binding key:
*.error.*matcheslog.error.database
It's great for matching a specific position in the key.
The Zero-or-More Wildcard: `#`
The hash (#) wildcard matches zero or more words in a routing key. It's much more powerful than *.
- Binding key:
log.#matcheslog.error,log.info.web,log.debug.cache.entry - Binding key:
animal.#matchesanimal.rabbit,animal.cat.sleepy
Use # to capture all messages that start with a certain pattern.
Producer: Declaring Topic Exchange
First, our producer needs to declare the Topic exchange. The type is simply "topic".
Try running this snippet to set up the exchange:
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
public class TopicProducerSetup {
private static final String EXCHANGE_NAME = "topic_logs";
public static void main(String[] argv) throws Exception {
ConnectionFactory factory = new ConnectionFactory();
factory.setHost("localhost"); // Connect to local RabbitMQ
try (Connection connection = factory.newConnection();
Channel channel = connection.createChannel()) {
channel.exchangeDeclare(EXCHANGE_NAME, "topic");
System.out.println("Topic exchange '" + EXCHANGE_NAME + "' declared.");
}
}
}Producer: Sending Messages
Now, let's send some messages using different routing keys. The exchange will use these keys to decide which queues receive the messages.
Notice how the keys are dot-separated, allowing for detailed categories.
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import java.nio.charset.StandardCharsets;
public class TopicMessageSender {
private static final String EXCHANGE_NAME = "topic_logs";
public static void main(String[] argv) throws Exception {
ConnectionFactory factory = new ConnectionFactory();
factory.setHost("localhost");
try (Connection connection = factory.newConnection();
Channel channel = connection.createChannel()) {
channel.exchangeDeclare(EXCHANGE_NAME, "topic");
sendMessage(channel, "animal.rabbit.fast", "A fast rabbit runs.");
sendMessage(channel, "animal.cat.sleepy", "A sleepy cat naps.");
sendMessage(channel, "log.error.db", "Database connection failed!");
sendMessage(channel, "log.info.web", "User logged in.");
System.out.println("Sent various topic messages.");
}
}
private static void sendMessage(Channel channel, String routingKey, String message) throws Exception {
channel.basicPublish(EXCHANGE_NAME, routingKey, null, message.getBytes(StandardCharsets.UTF_8));
System.out.println(" [x] Sent '" + routingKey + ":'" + message + "'");
}
}Consumer: Binding with `*`
Consumers bind their queues to the Topic exchange using binding keys that can contain wildcards. This consumer uses *.orange.*.
It will receive messages like animal.orange.fast but not fruit.apple.sweet or animal.orange.
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.DeliverCallback;
public class TopicConsumerOrange {
private static final String EXCHANGE_NAME = "topic_logs";
public static void main(String[] argv) throws Exception {
ConnectionFactory factory = new ConnectionFactory();
factory.setHost("localhost");
Connection connection = factory.newConnection();
Channel channel = connection.createChannel();
channel.exchangeDeclare(EXCHANGE_NAME, "topic");
String queueName = channel.queueDeclare().getQueue();
String bindingKey = "*.orange.*"; // Matches e.g., 'animal.orange.fast'
channel.queueBind(queueName, EXCHANGE_NAME, bindingKey);
System.out.println(" [x] Waiting for messages matching: '" + bindingKey + "'");
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 -> {});
}
}Consumer: Binding with `#`
This consumer uses the log.# binding key. This means it will receive all messages whose routing key starts with log., regardless of how many words follow.
This is extremely useful for systems like logging, where you might want a 'catch-all' listener for a category.
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.DeliverCallback;
public class TopicConsumerLogs {
private static final String EXCHANGE_NAME = "topic_logs";
public static void main(String[] argv) throws Exception {
ConnectionFactory factory = new ConnectionFactory();
factory.setHost("localhost");
Connection connection = factory.newConnection();
Channel channel = connection.createChannel();
channel.exchangeDeclare(EXCHANGE_NAME, "topic");
String queueName = channel.queueDeclare().getQueue();
String bindingKey = "log.#"; // Matches e.g., 'log.error.db', 'log.info.web'
channel.queueBind(queueName, EXCHANGE_NAME, bindingKey);
System.out.println(" [x] Waiting for messages matching: '" + bindingKey + "'");
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 -> {});
}
}Topic Exchange Use Cases
Topic exchanges shine in scenarios requiring flexible and hierarchical routing:
- Logging Systems: Route logs based on severity, source, and component (e.g.,
app.error.auth,app.info.payment). - Real-time Data Streams: Filter sensor data (e.g.,
sensor.room1.temp,sensor.room2.humidity). - Content Distribution: Deliver news articles to subscribers interested in specific categories or regions.
They provide fine-grained control over message flow.
Topic Routing Challenge
Consider the following messages and binding keys. Which messages will be delivered to a queue bound with the key animal.*.#.fast?
Recap: Topic Exchange Power
You've mastered the Topic exchange! It's an incredibly powerful tool for building flexible and scalable messaging architectures.
- Uses dot-separated routing keys.
*matches exactly one word.#matches zero or more words.- Ideal for logging, real-time analytics, and content filtering.
By using wildcards, you can create sophisticated routing rules to ensure messages go exactly where they're needed.
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Padroneggi l'exchange Topic per gestire pattern di routing complessi tramite il wildcard matching. Progetti topologie di routing dei messaggi flessibili e scalabili. Eserciti RabbitMQ Messaging & Async Systems con codice pratico che esegui direttamente nel browser, e un tutor IA 24/7 risponde alle tue domande mentre lavori sulla lezione.
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Tutte le lezioni di questo corso
- Exchange Fanout per Pub/Sub
- Exchange Direct per il routing
- Exchange Topic per un routing flessibile
- Exchange predefinito e binding impliciti