Spring @Configuration Annotation with Example

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In this article, we will discuss a very important Spring Java-based configuration annotation which is a @Configuration annotation with examples.

@Configuration Annotation Overview

Spring @Configuration annotation is part of the spring core framework. 

Spring @Configuration annotation indicates that the class has @Bean definition methods. So Spring container can process the class and generate Spring Beans to be used in the application.

Calls to @Bean methods on @Configuration classes can also be used to define inter-bean dependencies.

Importing Additional Configuration Classes

You need not put all your @Configuration into a single class. The @Import annotation can be used to import additional configuration classes. Alternatively, you can use @ComponentScan to automatically pick up all Spring components, including @Configuration classes.

 
Read more about @Import annotation on Spring @Import Annotation with Example

Refer below diagram shows an internal implementation for your reference:

@Configuration Annotation Example

The simplest possible @Configuration class would read as follows:

import org.springframework.boot.SpringApplication; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import com.companyname.projectname.customer.CustomerService; import com.companyname.projectname.order.OrderService; @Configuration public class Application { @Bean public CustomerService customerService() { return new CustomerService(); } @Bean public OrderService orderService() { return new OrderService(); } } 

The AppConfig class above would be equivalent to the following Spring XML:

<beans> <bean id="customerService" class="com.companyname.projectname.CustomerService"/> <bean id="orderService" class="com.companyname.projectname.OrderService"/> </beans>

Injecting inter-bean dependencies

When @Bean have dependencies on one another, expressing that dependency is as simple as having one bean method call another:

@Configuration public class AppConfig { @Bean public Foo foo() { return new Foo(bar()); } @Bean public Bar bar() { return new Bar(); } }

In the example above, the foo bean receives a reference to the bar via constructor 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