Asynchronous communication made easy: A guide to inter-microservice communication in Spring Boot (2024)

In today’s fast-paced world, it’s crucial for microservices to be able to communicate with each other efficiently and effectively. Asynchronous communication is a powerful way to enable microservices to collaborate without being blocked by long-running tasks or slow responses.

In this article, we will explore how to enable asynchronous communication between microservices in a Spring Boot application. We will look at several different approaches, including making asynchronous REST calls, using asynchronous messaging systems like Apache Kafka or RabbitMQ, and executing methods asynchronously.

By the end of this article, you will have a good understanding of the different options available for asynchronous communication in Spring Boot and be able to choose the best approach for your needs. So let’s get started!

There are several ways to enable asynchronous communication between microservices in a Spring Boot application. Here are a few options:

1. Asynchronous REST calls: You can use the AsyncRestTemplate class to make asynchronous REST calls to other microservices. This class is similar to the RestTemplate class, but it allows you to make non-blocking HTTP requests and returns a ResponseEntity object wrapped in a ListenableFuture object. You can then use the ListenableFuture object to retrieve the results of the REST call asynchronously.
2. Asynchronous messaging: You can use an asynchronous messaging system, such as Apache Kafka or RabbitMQ, to enable communication between microservices. In this approach, one microservice can publish a message to a message queue, and another microservice can consume the message and process it asynchronously. Spring Boot provides support for both Kafka and RabbitMQ through the spring-kafka and spring-rabbit libraries, respectively.
3. Asynchronous method execution: You can use the @Async annotation to annotate methods that should be executed asynchronously. When a method annotated with @Async is called, it will be executed in a separate thread, allowing the calling thread to continue executing. This can be useful for offloading time-consuming tasks to a separate thread, such as making a REST call or processing a large amount of data.

To enable communication between microservices using RabbitMQ in a Spring Boot application, you will need to include the spring-rabbit dependency in your project and configure a ConnectionFactory bean and a RabbitTemplate bean.

Here is an example of how you can configure RabbitMQ in a Spring Boot application:

import org.springframework.amqp.rabbit.connection.ConnectionFactory;
import org.springframework.amqp.rabbit.core.RabbitTemplate;
import org.springframework.amqp.support.converter.Jackson2JsonMessageConverter;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class RabbitConfiguration {
 @Bean
 public ConnectionFactory connectionFactory() {
 // Configure the connection factory using the RabbitMQ connection details
 CachingConnectionFactory connectionFactory = new CachingConnectionFactory();
 connectionFactory.setHost("localhost");
 connectionFactory.setPort(5672);
 connectionFactory.setUsername("rabbitmq");
 connectionFactory.setPassword("rabbitmq");
 return connectionFactory;
 }
 @Bean
 public RabbitTemplate rabbitTemplate(ConnectionFactory connectionFactory) {
 // Create a RabbitTemplate using the connection factory
 RabbitTemplate rabbitTemplate = new RabbitTemplate(connectionFactory);
 // Use Jackson to convert objects to JSON for the message body
 rabbitTemplate.setMessageConverter(new Jackson2JsonMessageConverter());
 return rabbitTemplate;
 }
}

Once you have configured the ConnectionFactory and RabbitTemplate beans, you can use the RabbitTemplate to send and receive messages from RabbitMQ.

Here is an example of how you can use the RabbitTemplate to send a message to a queue:

import org.springframework.amqp.core.AmqpTemplate;
import org.springframework.beans.factory.annotation.Autowired;
@Autowired
private AmqpTemplate amqpTemplate;
public void sendMessage(String queueName, Object message) {
 // Send the message to the specified queue
 amqpTemplate.convertAndSend(queueName, message);
}

In the example above, we use the convertAndSend() method of the AmqpTemplate object to send a message to the specified queue. The convertAndSend() method takes two arguments: the name of the queue and the message to send. The message will be converted to a JSON payload using the MessageConverter configured in the RabbitTemplate bean.

Here is an example of how you can use the RabbitTemplate to receive a message from a queue:

import org.springframework.amqp.core.AmqpTemplate;
import org.springframework.beans.factory.annotation.Autowired;
@Autowired
private AmqpTemplate amqpTemplate;
public Object receiveMessage(String queueName) {
 // Receive a message from the specified queue
 return amqpTemplate.receiveAndConvert(queueName);
}

In the example above, we use the receiveAndConvert() method of the AmqpTemplate object to receive a message from the specified queue. The receiveAndConvert() method takes the name of the queue as an argument and returns the message payload as an object. The payload will be converted from a JSON payload using the MessageConverter configured in the RabbitTemplate bean.

To enable communication between microservices using Apache Kafka in a Spring Boot application, you will need to include the spring-kafka dependency in your project and configure a KafkaTemplate bean.

Here is an example of how you can configure Kafka in a Spring Boot application:

To enable communication between microservices using Apache Kafka in a Spring Boot application, you will need to include the spring-kafka dependency in your project and configure a KafkaTemplate bean.

Here is an example of how you can configure Kafka in a Spring Boot application:

import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.clients.producer.ProducerConfig;
import org.apache.kafka.common.serialization.StringSerializer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.kafka.core.DefaultKafkaProducerFactory;
import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.kafka.core.ProducerFactory;
import java.util.HashMap;
import java.util.Map;
@Configuration
public class KafkaConfiguration {
 @Bean
 public ProducerFactory<String, String> producerFactory() {
 // Set the configuration properties for the producer
 Map<String, Object> configProps = new HashMap<>();
 configProps.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
 configProps.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
 configProps.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
 return new DefaultKafkaProducerFactory<>(configProps);
 }
 @Bean
 public KafkaTemplate<String, String> kafkaTemplate() {
 // Create a KafkaTemplate using the producer factory
 return new KafkaTemplate<>(producerFactory());
 }
}

Once you have configured the KafkaTemplate bean, you can use it to send and receive messages from Kafka.

Here is an example of how you can use the KafkaTemplate to send a message to a topic:

import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.beans.factory.annotation.Autowired;
@Autowired
private KafkaTemplate<String, String> kafkaTemplate;
public void sendMessage(String topic, String message) {
 // Send the message to the specified topic
 kafkaTemplate.send(topic, message);
}

In the example above, we use the send() method of the KafkaTemplate object to send a message to the specified topic. The send() method takes two arguments: the name of the topic and the message to send. The message will be serialized using the Serializer configured in the ProducerFactory bean.

To receive messages from a Kafka topic, you can create a KafkaListener bean and use the @KafkaListener annotation to specify the topic to listen to.

Here is an example of how you can use the @KafkaListener annotation to receive messages from a topic:

import org.springframework.kafka.annotation.KafkaListener;
import org.springframework.stereotype.Component;
@Component
public class KafkaConsumer {
 @KafkaListener(topics = "my-topic")
 public void receiveMessage(String message) {
 // Process the received message
 System.out.println("Received message: " + message);
 }
}

In the example above, we have annotated the receiveMessage() method with the @KafkaListener annotation and specified the topic to listen to. The receiveMessage() method will be called whenever a message is received on the specified topic, and the message payload will be passed as an argument to the method. The payload will be deserialized using the Deserializer configured in the ConsumerFactory bean.

You can use the @KafkaListener annotation on any method that you want to use as a message listener. You can also specify multiple topics to listen to by separating the topic names with a comma, like this: @KafkaListener(topics = "topic1,topic2").

In conclusion, asynchronous communication is an essential tool for enabling microservices to collaborate effectively. In this article, we explored several different approaches for enabling asynchronous communication in Spring Boot, including making asynchronous REST calls, using asynchronous messaging systems like Apache Kafka or RabbitMQ, and executing methods asynchronously. By understanding the options available and choosing the best approach for your needs, you can ensure that your microservices are able to communicate efficiently and effectively.

I hope you found this article helpful and that it gave you a good understanding of the different options for asynchronous communication in Spring Boot. If you have any questions or would like to learn more, please don’t hesitate to reach out. Thanks for reading!