Micronaut: Publish and listen on custom events

In this post, I am going to explain how to publish and listen on custom events in Micronaut.

 

Define an event class.

public class ConnectionCreateEvent {
	private String message;

	public ConnectionCreateEvent(String message) {
		this.message = message;
	}

	public String getMessage() {
		return message;
	}

	public void setMessage(String message) {
		this.message = message;
	}
}

 

Define a publisher bean that emit the ConnectionCreateEvent messages.

@Singleton
public class ConnectionCreateEventPublisher {
	
	@Inject
	ApplicationEventPublisher<ConnectionCreateEvent> eventPublisher;

	public void publishEvent(String message) {
		eventPublisher.publishEvent(new ConnectionCreateEvent(message));
	}
}

Define a listener for ConnectionCreateEvents. To listen to an event, register a bean that implements ApplicationEventListener where the generic type is the type of event.

@Singleton
public class ConnectionCreateEventListener implements ApplicationEventListener<ConnectionCreateEvent> {

	@Override
	public void onApplicationEvent(ConnectionCreateEvent event) {
		System.out.println("message : '" + event.getMessage() + "'");
	}

}

Find the below working application.

 

Step 1: Create new maven project ‘micronaut-publish-listen-events’.

 

Step 2: Update pom.xml with maven dependencies.

 

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.sample.app</groupId>
	<artifactId>micronaut-publish-listen-events</artifactId>
	<version>1</version>

	<properties>
		<maven-compiler-plugin.version>3.8.1</maven-compiler-plugin.version>
		<micronaut.version>3.7.1</micronaut.version>
		<slf4j.version>2.0.3</slf4j.version>

		<maven.compiler.target>15</maven.compiler.target>
		<maven.compiler.source>15</maven.compiler.source>
	</properties>

	<dependencies>

		<dependency>
			<groupId>io.micronaut</groupId>
			<artifactId>micronaut-inject-java</artifactId>
			<version>${micronaut.version}</version>
		</dependency>

		<dependency>
			<groupId>org.slf4j</groupId>
			<artifactId>slf4j-api</artifactId>
			<version>${slf4j.version}</version>
		</dependency>
		<dependency>
			<groupId>org.slf4j</groupId>
			<artifactId>slf4j-simple</artifactId>
			<version>${slf4j.version}</version>
		</dependency>
	</dependencies>

	<build>
		<plugins>

			<plugin>
				<artifactId>maven-assembly-plugin</artifactId>
				<configuration>
					<archive>
						<manifest>
							<mainClass>com.sample.app.App</mainClass>
						</manifest>
					</archive>
					<descriptorRefs>
						<descriptorRef>jar-with-dependencies</descriptorRef>
					</descriptorRefs>
				</configuration>

				<executions>
					<execution>
						<id>make-assembly</id>
						<phase>package</phase>
						<goals>
							<goal>single</goal>
						</goals>
					</execution>
				</executions>
			</plugin>

		</plugins>
	</build>
</project>

Step 3: Define ConnectionCreateEvent class.

 

ConnectionCreateEvent.java

package com.sample.app.event;

public class ConnectionCreateEvent {
	private String message;

	public ConnectionCreateEvent(String message) {
		this.message = message;
	}

	public String getMessage() {
		return message;
	}

	public void setMessage(String message) {
		this.message = message;
	}
}

Step 4: Define event publisher.

 

ConnectionCreateEventPublisher.java

package com.sample.app.event.publishers;

import com.sample.app.event.ConnectionCreateEvent;

import io.micronaut.context.event.ApplicationEventPublisher;
import jakarta.inject.Inject;
import jakarta.inject.Singleton;

@Singleton
public class ConnectionCreateEventPublisher {
	
	@Inject
	ApplicationEventPublisher<ConnectionCreateEvent> eventPublisher;

	public void publishEvent(String message) {
		eventPublisher.publishEvent(new ConnectionCreateEvent(message));
	}
}

Step 5: Define event listener.

 

ConnectionCreateEventListener.java

package com.sample.app.event.listeners;

import com.sample.app.event.ConnectionCreateEvent;

import io.micronaut.context.event.ApplicationEventListener;
import jakarta.inject.Singleton;

@Singleton
public class ConnectionCreateEventListener implements ApplicationEventListener<ConnectionCreateEvent> {

	@Override
	public void onApplicationEvent(ConnectionCreateEvent event) {
		System.out.println("message : '" + event.getMessage() + "'");
	}

}

Step 6: Define main application class.

 

App.java

package com.sample.app;

import com.sample.app.event.publishers.ConnectionCreateEventPublisher;

import io.micronaut.context.ApplicationContext;

public class App {

	public static void main(String[] args) {
		try (ApplicationContext applicationContext = ApplicationContext.run()) {
			ConnectionCreateEventPublisher connectionCreateEventPublisher = applicationContext.getBean(ConnectionCreateEventPublisher.class);

			connectionCreateEventPublisher.publishEvent("Connection1 created");
			connectionCreateEventPublisher.publishEvent("Connection2 created");
			connectionCreateEventPublisher.publishEvent("Connection3 created");
		}

	}
}

Total project structure looks like below.

Build the project using mvn package command.

Navigate to the folder where pom.xml is located and execute the command ‘mvn package’.

Upon command successful execution, you can see the jar file ‘micronaut-publish-listen-events-1-jar-with-dependencies.jar’ in project target folder.

$ ls ./target/
archive-tmp
classes
generated-sources
maven-archiver
maven-status
micronaut-publish-listen-events-1-jar-with-dependencies.jar
micronaut-publish-listen-events-1.jar
test-classes

Execute below command to run the application.

java -jar ./target/micronaut-publish-listen-events-1-jar-with-dependencies.jar

$ java -jar ./target/micronaut-publish-listen-events-1-jar-with-dependencies.jar
message : 'Connection1 created'
message : 'Connection2 created'
message : 'Connection3 created'

You can download this application from this link.

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