Micronaut: Produce a bean from primitive types

You can produce a bean from primitive type using @Bean annotation.

@Factory
public class BeansFactory {

	@Bean
	@Named("pi")
	Double PI = 3.14;

	@Bean
	@Named("appName")
	String appName = "chat server";
}

Primitive beans has following limitations.

a.   AOP advice cannot be applied to primitives or wrapper types

b.   Due to the above custom scopes that proxy are not supported

c.    The @Bean(preDestroy=..) member is not supported

 

Find the below working application.

 

Step 1: Create new maven project ‘micronaut-produce-bean-from-primitive-type’.

 

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-produce-bean-from-primitive-type</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 BeansFactory class.

 

BeansFactory.java

package com.sample.app.factories;

import io.micronaut.context.annotation.Bean;
import io.micronaut.context.annotation.Factory;
import jakarta.inject.Named;

@Factory
public class BeansFactory {

	@Bean
	@Named("pi")
	Double PI = 3.14;

	@Bean
	@Named("appName")
	String appName = "chat server";
}

Step 4: Define main application class.

 

App.java

package com.sample.app;

import io.micronaut.context.ApplicationContext;
import io.micronaut.inject.qualifiers.Qualifiers;;

public class App {

	public static void main(String[] args) {
		try (ApplicationContext applicationContext = ApplicationContext.run()) {
			Double pi = applicationContext.getBean(Double.class,
					Qualifiers.byName("pi"));
			String appName = applicationContext.getBean(String.class,
					Qualifiers.byName("appName"));

			System.out.println("pi : " + pi);
			System.out.println("appName : " + appName);
		}
	}
}

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-produce-bean-from-primitive-type-1-jar-with-dependencies.jar’ in project target folder.

$ ls ./target/
archive-tmp
classes
generated-sources
maven-archiver
maven-status
micronaut-produce-bean-from-primitive-type-1-jar-with-dependencies.jar
micronaut-produce-bean-from-primitive-type-1.jar
test-classes

Run the jar file ‘micronaut-produce-bean-from-primitive-type-1-jar-with-dependencies.jar’ by executing below command.

$ java -jar ./target/micronaut-produce-bean-from-primitive-type-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.
pi : 3.14
appName : chat server

You can download this application from this link.

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