Spring Cloud Stream with RabbitMQ – Functional style!
Spring Cloud Stream is a framework that simplifies the development of event-driven applications by providing abstractions for common messaging patterns. It uses a message broker, such as RabbitMQ or Kafka, to facilitate communication between different parts of the application. In this tutorial, we’ll focus on how to use functional style producers and consumers with Spring Cloud Stream.
Functional style producers and consumers are a new feature in Spring Cloud Stream 3.0 that allows you to define producers and consumers using functional programming constructs. This makes it easier to write concise and readable code for sending and receiving messages.
To get started with functional style producers and consumers, you’ll need to add the Spring Cloud Stream and message broker dependencies to your project. Here’s an example of how to add the RabbitMQ dependency to your project’s build.gradle file:
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dependencies { implementation 'org.springframework.cloud:spring-cloud-stream' implementation 'org.springframework.cloud:spring-cloud-stream-binder-rabbit' } |
Once you’ve added the dependencies, you can create a functional style producer by defining a function that takes a MessageBuilder and returns a Message. The MessageBuilder provides a convenient way to create messages with headers and payloads. Here’s an example of a simple producer that sends a message to a RabbitMQ exchange:
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import org.springframework.messaging.Message; import org.springframework.messaging.support.MessageBuilder; import org.springframework.stereotype.Component; import java.util.function.Supplier; @Component public class MyProducer implements Supplier<Message<String>> { @Override public Message<String> get() { String payload = "Hello, world!"; return MessageBuilder.withPayload(payload).build(); } } |
In this example, the MyProducer class implements the Supplier interface, which means it provides a single method that returns a message. The get() method creates a new Message using MessageBuilder and sets the payload to “Hello, world!”.
To create a functional style consumer, you can define a function that takes a Message and returns void. The function can then process the message as needed. Here’s an example of a simple consumer that prints the message payload to the console:
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import org.springframework.messaging.Message; import org.springframework.stereotype.Component; import java.util.function.Consumer; @Component public class MyConsumer implements Consumer<Message<String>> { @Override public void accept(Message<String> message) { System.out.println("Received message: " + message.getPayload()); } } |
In this example, the MyConsumer class implements the Consumer interface, which means it provides a single method that accepts a message. The accept() method simply prints the payload of the message to the console.
To connect the producer and consumer to a RabbitMQ exchange, you’ll need to configure the binding between them. This can be done using properties in the application.yml file. Here’s an example of how to configure the binding between the MyProducer and MyConsumer classes:
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spring: cloud: stream: function: definition: myProducer;myConsumer bindings: myProducer-out-0: destination: myExchange producer: required-groups: myGroup myConsumer-in-0: destination: myExchange group: myGroup |
In this example, the function definition property specifies that the myProducer and myConsumer functions should be used as the producer and consumer, respectively. The bindings property configures the bindings between the producer and consumer. The myProducer-out-0 binding sends messages to the myExchange exchange with the required group set to myGroup. The myConsumer-in-0 binding receives messages from the myExchange exchange with the group set to myGroup.
With the bindings configured, you can now run the Spring Boot application and start sending and receiving messages. Here’s an example of how to run the application:
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import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; @SpringBootApplication public class MyApp { public static void main(String[] args) { SpringApplication.run(MyApp.class, args); } } |
Once the application is running, the MyProducer class will automatically start sending messages to the RabbitMQ exchange. The MyConsumer class will automatically start receiving messages from the same exchange.
And that’s it! You’ve now learned how to use Spring Cloud Stream and functional style producers and consumers to send and receive messages with a message broker. With this knowledge, you can start building event-driven applications that are scalable, reliable, and easy to maintain.
