Micronaut: Qualify a bean by name

In this post, I am going to explain how to qualify a bean by name.

public interface Dog {

	String aboutMe();
}

@Singleton
public class BullDog implements Dog {

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

}

@Singleton
public class PoodleDog implements Dog {

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

}

@Singleton
public class DogService {

	private Dog dog1;
	private Dog dog2;

	public DogService (@Named("Bull") Dog dog1, @Named("Poodle") Dog dog2) {
		this.dog1 = dog1;
		this.dog2 = dog2;
	}
}

 

Above snippet defines

a. The Dog interface defines the common contract

b. The BullDog class is the first implementation

c. The PoodleDog class is the second implementation

 

public DogService (@Named("Bull") Dog dog1, @Named("Poodle") Dog dog2)

dog1 is injected with an instance of BullDog and dog2 is injected with an instance of PoodleDog.

 

 

How is this injection possible?

@Named("Bull") Dog dog1;

@Named qualifier value (Bull) + type being injected simple name (Dog) == (case-insensitive) == The simple name of a bean of type Engine (BullDog).

 

Find the below working application.

 

Step 1: Create new maven project ‘micronaut-qualify-by-name’.

 

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-qualify-by-name</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.Singleton;

@Singleton
public class BullDog implements Dog {

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

}

PoodleDog.java

package com.sample.app.models;

import com.sample.app.interfaces.Dog;

import jakarta.inject.Singleton;

@Singleton
public class PoodleDog implements Dog {

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

}

Step 5: DefineDogService class.

 

DogService.java

package com.sample.app.util;

import com.sample.app.interfaces.Dog;

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

@Singleton
public class DogService {

	private Dog dog1;
	private Dog dog2;

	public DogService(@Named("Bull") Dog dog1, @Named("Poodle") Dog dog2) {
		this.dog1 = dog1;
		this.dog2 = 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.util.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-qualify-by-name-1-jar-with-dependencies.jar’ in project target folder.

 

$ls ./target/
archive-tmp						maven-status
classes							micronaut-qualify-by-name-1-jar-with-dependencies.jar
generated-sources					micronaut-qualify-by-name-1.jar
maven-archiver						test-classes

 

Run the jar file by executing below command.

java -jar ./target/micronaut-qualify-by-name-1-jar-with-dependencies.jar

$java -jar ./target/micronaut-qualify-by-name-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.
I am Bull Dog
I am Poodle Dog

 

You can download this application from this link.

 

Note

You can also declare @Named annotation at the class level of a bean to explicitly define the name of the bean.

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

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

}

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

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

}

@Singleton
public class DogService {

	private Dog dog1;
	private Dog dog2;

	public DogService(@Named("myBullDog") Dog dog1, @Named("myPoodlelDog") Dog dog2) {
		this.dog1 = dog1;
		this.dog2 = dog2;
	}

	public void aboutMe() {

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

	}

}

 

  

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