Micronaut: introspection: static creator methods

The @Creator annotation can be applied to static methods to create class instances.

@Introspected
public class Person {

	public Integer id;

	public String name;

	private Person(Integer id, String name) {
		this.id = id;
		this.name = name;
	}

	@Creator
	public static Person getPerson() {
		System.out.println("Default constructor called");
		return new Person(-1, "no_name");
	}

	@Creator
	public static Person getPerson(Integer id, String name) {
		System.out.println("Constructor with two arguments called");
		return new Person(id, name);
	}

}

Find the below working application.

 

Step 1: Create new maven project ‘micronaut-introspect-static-creator-methods’.

 

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-introspect-static-creator-methods</artifactId>
	<version>1</version>

	<properties>
		<maven-compiler-plugin.version>3.8.1</maven-compiler-plugin.version>
		<micronaut.version>3.7.2</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>${micronaut.version}</version>
		</dependency>
		<dependency>
			<groupId>io.micronaut</groupId>
			<artifactId>micronaut-runtime</artifactId>
			<version>${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 Person model class.

 

Person.java

package com.sample.app.model;

import io.micronaut.core.annotation.Creator;
import io.micronaut.core.annotation.Introspected;

@Introspected
public class Person {

	public Integer id;

	public String name;

	private Person(Integer id, String name) {
		this.id = id;
		this.name = name;
	}

	@Creator
	public static Person getPerson() {
		System.out.println("Default constructor called");
		return new Person(-1, "no_name");
	}

	@Creator
	public static Person getPerson(Integer id, String name) {
		System.out.println("Constructor with two arguments called");
		return new Person(id, name);
	}

	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

}

Step 4: Define main application class.

 

App.java

package com.sample.app;

import com.sample.app.model.Person;

import io.micronaut.context.ApplicationContext;
import io.micronaut.core.beans.BeanIntrospection;

public class App {

	public static void main(String[] args) {
		try (ApplicationContext applicationContext = ApplicationContext.run()) {

			final BeanIntrospection<Person> introspection = BeanIntrospection.getIntrospection(Person.class);
			Person person = introspection.instantiate(1, "Krishna");

			System.out.println("id : " + person.id);
			System.out.println("name : " + person.name + "\n");

			person = introspection.instantiate();
			System.out.println("id : " + person.id);
			System.out.println("name : " + person.name);

		}

	}
}

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-introspect-static-creator-methods-1-jar-with-dependencies.jar’ in project target folder.

$ls ./target/
archive-tmp
classes
generated-sources
maven-archiver
maven-status
micronaut-introspect-static-creator-methods-1-jar-with-dependencies.jar
micronaut-introspect-static-creator-methods-1.jar
test-classes

Execute below command to run the application.

java -jar ./target/micronaut-introspect-static-creator-methods-1-jar-with-dependencies.jar

$java -jar ./target/micronaut-introspect-static-creator-methods-1-jar-with-dependencies.jar
Constructor with two arguments called
id : 1
name : Krishna

Default constructor called
id : -1
name : no_name

You can download this application from this link.

 

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