Spring @Autowired Annotation Example

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In this article, we will learn @Autowired annotation to inject the dependency automatically using Constructor injection, Setter injection, and Field injection.

@Autowired Annotation Overview

The @Autowired annotation is used to inject the bean automatically.

The @Autowired annotation is used in Constructor injection, Setter injection, and Field injection.

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Constructor Injection using @Autowired Annotation

Let's create Interfaces and classes required to demonstrate @Autowired annotation.

Pizza Interface

package net.javaguides.springboot.service; public interface Pizza { String getPizza(); }

VegPizza Class

package net.javaguides.springboot.service; import org.springframework.stereotype.Component; @Component public class VegPizza implements Pizza{ @Override public String getPizza() { return "Veg Pizza"; } }

NonVegPizza

package net.javaguides.springboot.service; import org.springframework.stereotype.Component; @Component public class NonVegPizza implements Pizza{ @Override public String getPizza() { return "Non-veg Pizza"; } }

PizzaController Class - Constructor Injection using @Autowired Annotation

package net.javaguides.springboot.controller; import net.javaguides.springboot.service.Pizza; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.beans.factory.annotation.Qualifier; import org.springframework.stereotype.Component; @Component public class PizzaController { private Pizza pizza; @Autowired public PizzaController(@Qualifier("vegPizza") Pizza pizza) { System.out.println("inside PizzaController constructor"); this.pizza = pizza; } public String getPizza(){ return pizza.getPizza(); } }

In this above code snippet, we are using @Autowired annotation to inject VegPizza dependency in PizzaController class using constructor injection. Note that we are using @Qualifier annotation in conjunction with @Autowired to avoid confusion when we have two or more beans configured for the same type.

Constructor injection using @Autowired annotation:

 @Autowired public PizzaController(@Qualifier("vegPizza") Pizza pizza) { System.out.println("inside PizzaController constructor"); this.pizza = pizza; }

Testing

Let's retrieve the PizzaController spring bean from the ApplicationContext and call its method:

package net.javaguides.springboot; import net.javaguides.springboot.controller.PizzaController; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import java.util.Arrays; @SpringBootApplication public class SpringbootDockerDemoApplication {	public static void main(String[] args) {	var context = SpringApplication.run(SpringbootDockerDemoApplication.class, args);	System.out.println("calling pizzaController.getPizza()");	PizzaController pizzaController = context.getBean(PizzaController.class);	String message = pizzaController.getPizza();	System.out.println(message);	} }

Output:

calling pizzaController.getPizza() Veg Pizza

Setter Injection using @Autowired Annotation

Let's use Setter Injection with @Autowired Annotation to inject VegPizza bean in PizzaController class:

package net.javaguides.springboot.controller; import net.javaguides.springboot.service.Pizza; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.beans.factory.annotation.Qualifier; import org.springframework.stereotype.Component; @Component public class PizzaController { private Pizza pizza; // @Autowired // public PizzaController(@Qualifier("vegPizza") Pizza pizza) { // System.out.println("inside PizzaController constructor"); // this.pizza = pizza; // } // setter injection @Autowired @Qualifier("vegPizza") public void setPizza(Pizza pizza) { this.pizza = pizza; } public String getPizza(){ return pizza.getPizza(); } }

In this above code snippet, we are using @Autowired annotation to inject VegPizza dependency in PizzaController class using setter injection. Note that we are using @Qualifier annotation in conjunction with @Autowired to avoid confusion when we have two or more beans configured for the same type.

Setter injection using @Autowired annotation:

 @Autowired @Qualifier("vegPizza") public void setPizza(Pizza pizza) { this.pizza = pizza; }

Testing

Let's retrieve the PizzaController spring bean from the ApplicationContext and call its method:

package net.javaguides.springboot; import net.javaguides.springboot.controller.PizzaController; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import java.util.Arrays; @SpringBootApplication public class SpringbootDockerDemoApplication {	public static void main(String[] args) {	var context = SpringApplication.run(SpringbootDockerDemoApplication.class, args);	System.out.println("calling pizzaController.getPizza()");	PizzaController pizzaController = context.getBean(PizzaController.class);	String message = pizzaController.getPizza();	System.out.println(message);	} }

Output:

calling pizzaController.getPizza() Veg Pizza

Field Injection using @Autowired Annotation

Let's use Field Injection with @Autowired Annotation to inject VegPizza bean in PizzaController class:

package net.javaguides.springboot.controller; import net.javaguides.springboot.service.Pizza; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.beans.factory.annotation.Qualifier; import org.springframework.stereotype.Component; @Component public class PizzaController { @Autowired @Qualifier("vegPizza") private Pizza pizza; // @Autowired // public PizzaController(@Qualifier("vegPizza") Pizza pizza) { // System.out.println("inside PizzaController constructor"); // this.pizza = pizza; // } // // setter injection // @Autowired // @Qualifier("vegPizza") // public void setPizza(Pizza pizza) { // this.pizza = pizza; // } public String getPizza(){ return pizza.getPizza(); } }

In this above code snippet, we are using @Autowired annotation to inject VegPizza dependency in PizzaController class using field injection. Note that we are using @Qualifier annotation in conjunction with @Autowired to avoid confusion when we have two or more beans configured for the same type.

Field injection using @Autowired annotation:

 @Autowired @Qualifier("vegPizza") private Pizza pizza;

Testing

Let's retrieve the PizzaController spring bean from the ApplicationContext and call its method:

package net.javaguides.springboot; import net.javaguides.springboot.controller.PizzaController; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import java.util.Arrays; @SpringBootApplication public class SpringbootDockerDemoApplication {	public static void main(String[] args) {	var context = SpringApplication.run(SpringbootDockerDemoApplication.class, args);	System.out.println("calling pizzaController.getPizza()");	PizzaController pizzaController = context.getBean(PizzaController.class);	String message = pizzaController.getPizza();	System.out.println(message);	} }

Output:

calling pizzaController.getPizza() Veg Pizza

Conclusion

In this article, we learned @Autowired annotation to inject the dependency automatically using Constructor injection, Setter injection, and Field injection.

Related Spring and Spring Boot Annotations

• Spring Boot @Bean Annotation Example
• Spring @Qualifier Annotation Example
• Spring @Autowired Annotation with Example
• Spring @Bean Annotation with Example
• Spring @Configuration Annotation with Example
• Spring @PropertySource Annotation with Example
• Spring @Import Annotation with Example
• Spring @ImportResource Annotation Example
• Spring - @Lazy Annotation Example
• Spring - @Primary Annotation Example
• Spring @PostConstruct and @PreDestroy Example
• Spring @Repository Annotation
• Spring @Service Annotation 
• The Spring @Controller and @RestController Annotations
• Spring Boot @Component, @Controller, @Repository and @Service
• Spring @Scope annotation with Prototype Scope Example
• Spring @Scope annotation with Singleton Scope Example
• Spring Boot @PathVariable
• Spring Boot @ResponseBody
• Spring @RequestBody - Binding Method Parameters to Request Body
• Spring Boot @ResponseStatus Annotation
• Spring Boot - Creating Asynchronous Methods using @Async Annotation
• @SpringBootTest Spring Boot Example
• @SpringBootTest vs @WebMvcTest
• @DataJpaTest Spring Boot Example
• Spring @PostConstruct and @PreDestroy Example
• Spring @GetMapping, @PostMapping, @PutMapping, @DeleteMapping and @PatchMapping
• Spring Boot @EnableAutoConfiguration Annotation with Example
• Spring Boot @SpringBootApplication Annotation with Example