Micronaut: Specify the constructor to use for introspection

For classes with multiple constructors, apply the @Creator annotation to specify the constructor to use for introspection.

@Introspected
public class Person {

	public Integer id;

	public String name;

	public Person(String name) {
		this.name = name;
	}

	@Creator
	public Person(Integer id, String name) {
		this.id = id;
		this.name = name;
	}

}

 

Find the below working application.

 

Step 1: Create new maven project ‘micronaut-introspect-specify-constructor’.

 

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-specify-constructor</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 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;

	public Person(String name) {
		this.name = name;
	}

	@Creator
	public Person(Integer id, String name) {
		this.id = id;
		this.name = 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;
import io.micronaut.core.beans.BeanProperty;

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);

			final BeanProperty<Person, String> property = introspection.getRequiredProperty("name", String.class);
			property.set(person, "Ram");
			String name = property.get(person);

			System.out.println("\nname : " + name);
			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-specify-constructor-1-jar-with-dependencies.jar’ in project target folder.

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

Execute below command to run the application.

java -jar ./target/micronaut-introspect-specify-constructor-1-jar-with-dependencies.jar

$java -jar ./target/micronaut-introspect-specify-constructor-1-jar-with-dependencies.jar
id : 1
name : Krishna

name : Ram
id : 1
name : Ram

You can download this application from this link.

 

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