Micronaut: inject a bean using @Inject annotation

@Inject annotation is used to inject a bean to Micronaut managed beans. @Inject annotation identifies injectable constructors, methods, and fields, may apply to static as well as instance members. An injectable member may have any access modifier (private, package-private, protected, public). Constructors are injected first, followed by fields, and then methods. Fields and methods in superclasses are injected before those in subclasses.

 

Example

@Singleton
public class DogService {

	@Inject
	@Named("myBullDog")
	private Dog dog1;

	@Inject
	@Named("myPoodleDog")
	private Dog dog2;

	......
	......
}

Find the below working application.

 

Step 1: Create new maven project ‘micronaut-inject-annotation-demo’.

 

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-inject-annotation-demo</artifactId>
	<version>1</version>

	<properties>
		<maven-compiler-plugin.version>3.8.1</maven-compiler-plugin.version>
		<micronaut.version>3.7.1</micronaut.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>
	</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 Dog interface.

 

Dog.java

package com.sample.app.interfaces;

public interface Dog {

	String aboutMe();
}

 

Step 4: Define BullDog and PoodleDog classes.

 

BullDog.java

package com.sample.app.models;

import com.sample.app.interfaces.Dog;

import jakarta.inject.Named;
import jakarta.inject.Singleton;

@Singleton
@Named("myBullDog")
public class BullDog implements Dog {

	@Override
	public String aboutMe() {
		return "Bull Dog";
	}

}

 

PoodleDog.java

package com.sample.app.models;

import com.sample.app.interfaces.Dog;

import jakarta.inject.Named;
import jakarta.inject.Singleton;

@Singleton
@Named("myPoodleDog")
public class PoodleDog implements Dog {

	@Override
	public String aboutMe() {
		return "Poodle Dog";
	}

}

 

Step 5: Define DogService class.

 

DogService.java

 

package com.sample.app.service;

import com.sample.app.interfaces.Dog;

import jakarta.inject.Inject;
import jakarta.inject.Named;
import jakarta.inject.Singleton;

@Singleton
public class DogService {

	@Inject
	@Named("myBullDog")
	private Dog dog1;

	@Inject
	@Named("myPoodleDog")
	private Dog dog2;

	public void aboutMe() {

		System.out.println(dog1.aboutMe());
		System.out.println(dog2.aboutMe());

	}

}

 

Step 6: Define main application class.

 

App.java

 

package com.sample.app;

import com.sample.app.service.DogService;

import io.micronaut.context.ApplicationContext;

public class App {

	public static void main(String[] args) {
		try (ApplicationContext context = ApplicationContext.run()) {
			DogService animalUtil = context.getBean(DogService.class);
			animalUtil.aboutMe();
		}
	}
}

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-inject-annotation-demo-1-jar-with-dependencies.jar’ in project target folder.

$ ls ./target/
archive-tmp
classes
generated-sources
maven-archiver
maven-status
micronaut-inject-annotation-demo-1-jar-with-dependencies.jar
micronaut-inject-annotation-demo-1.jar
test-classes

Execute below command to run the application.

java -jar ./target/micronaut-inject-annotation-demo-1-jar-with-dependencies.jar

$ java -jar ./target/micronaut-inject-annotation-demo-1-jar-with-dependencies.jar
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
Bull Dog
Poodle Dog

You can download this application from this link.

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