@Primary Annotation in Spring with Example

In this article we will learn about the @Primary Annotation in Spring with a very simple example.

Let’s first try to understand why and when we need this @Primary annotation. In real life scenarios, we encounter use cases, where we find multiple auto-wiring candidates for the same type. In these cases, we can use @Primary annotation to give preference to a particular bean, so that it becomes the autowired value by default. We can use @Qualifier annotation for autowiring other non primary beans.

We will take a simple example of a Car. Hatchback, Sedan and Van being the types of Car.

Here, We will assign the precedence to Hatchback bean by annotating it with @Primary.

Let’s get started then without much ado.

Technology Stack

Spring Core and Spring Boot

Project Structure

@Primary Annotation in Spring with Example

<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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>SpringPrimary</groupId>
	<artifactId>SpringPrimary</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.2.1.RELEASE</version>
		<relativePath />
	</parent>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
	</dependencies>
</project>

package com.spring.beans;

public interface Car {
	
	String type();
	
}

package com.spring.beans;

import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Component;

@Component
@Primary
public class Hatchback implements Car{

	@Override
	public String type() {
		return "Hatchback";
	}

}

package com.spring.beans;

import org.springframework.stereotype.Component;

@Component
public class Sedan implements Car{

	@Override
	public String type() {
		return "Sedan";
	}

}

package com.spring.beans;

import org.springframework.stereotype.Component;

@Component
public class Van implements Car{

	@Override
	public String type() {
		return "Van";
	}

}

package com.spring.config;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import com.spring.beans.Car;

@SpringBootApplication(scanBasePackages="com.spring.beans")
public class Application implements CommandLineRunner{

	
	// This will inject the bean of the component which is marked with @Primary 
	@Autowired
	private Car car;
	
	//Wiring Sedan bean by using Qualifier
	@Autowired
	@Qualifier("sedan")
	private Car sedan;
	
	//Wiring Van bean by using Qualifier
	@Autowired
	@Qualifier("van")
	private Car van;
	
	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
	}
	

	@Override
	public void run(String... args) throws Exception {
		System.out.println(car.type());
		System.out.println(sedan.type());
		System.out.println(van.type());
		System.exit(1);
	}

}