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Spring – @Import annotation

In this guide we will see how to use the Spring @Import annotation, importing multiple configuration classes, and we will see difference between @Import vs @ComponentScan.

@Import annotation in Spring allows you to load bean definitions from one or more another @Configuration files or Components. You might not want to configure all the beans in one configuration file. Using @Import we can split the configurations across multiple configuration files for modularising, that makes our code more cleaner and maintainable.

1. Creating Configuration classes

First let’s create configuration classes and then import them to another configurations. Here we are creating FishConfig and BirdConfig configuration files, they having GoldFish, Guppy, Salmon, Eagle, Ostrich, Peacock bean definitions.

Creating Configuration classes:

@Configuration
public class FishConfig {

	@Bean
	public GoldFish goldFish() {
		return new GoldFish();
	}
	
	@Bean
	public Guppy guppy() {
		return new Guppy();
	}
	
	@Bean
	public Salmon salmon() {
		return new Salmon();
	}
	
}
@Configuration
public class BirdConfig {

	@Bean
	public Eagle eagle() {
		return new Eagle();
	}
	
	@Bean
	public Ostrich ostrich() {
		return new Ostrich();
	}
	
	@Bean
	public Peacock peacock() {
		return new Peacock();
	}
}

2. Using @Import annotation

Now, Let’s import the FishConfig and BirdConfig files into another configuration called ImportBeansConfig. @Import annotation allows grouping/importing multiple configurations also.

In following example we are defining ExampleBean and Sample beans for testing imported configurations.

@Configuration
@Import({FishConfig.class, BirdConfig.class})
public class ImportBeansConfig {

	@Bean
	public ExampleBean exampleBean() {
		return new ExampleBean();
	}
	
	@Bean
	public SampleBean sampleBean() {
		return new SampleBean();
	}
}
public class ExampleBean {
	
	@Autowired
	private Salmon salmon;
	
	@Autowired
	private Guppy guppy;
	
	@Autowired
	private Peacock peacock;
	
	public void printObjects() {
		System.out.println("---------- Print ExampleBean Objects ----------");
		System.out.println(salmon);
		System.out.println(guppy);
		System.out.println(peacock);
	}
}
public class SampleBean {
	
	@Autowired
	private GoldFish goldFish;
	
	@Autowired
	private Eagle eagle;
	
	@Autowired
	private Ostrich ostrich;
	
	public void printObjects() {
		System.out.println("---------- Print SampleBean Objects ----------");
		System.out.println(goldFish);
		System.out.println(eagle);
		System.out.println(ostrich);
	}
	
}

Testing @Import:

public class ImportAnnotationConfigDemo {

	public static void main(String[] args) {
		ApplicationContext ctxt = new AnnotationConfigApplicationContext(ImportBeansConfig.class);

		ExampleBean exampleBean = ctxt.getBean(ExampleBean.class);
		SampleBean sampleBean = ctxt.getBean(SampleBean.class);
		
		exampleBean.printObjects();
		sampleBean.printObjects();
		
	}
}

Output Results:

---------- Print ExampleBean Objects ----------
Salmon
Guppy
Peacock
---------- Print SampleBean Objects ----------
GoldFish
Eagle
Ostrich

3. Importing Components

@Import annotation allowed to import specific component into other configuration. We can import group/multiple components. Let’s see example, in the following example ExampleComponent importing into ImportComponentsConfig which defined bean called ComponentsTestBean.

@Configuration
@Import(ExampleComponent.class)
public class ImportComponentsConfig {

	@Bean
	public ComponentsTestBean componentsTestBean() {
		return new ComponentsTestBean();
	}
}

Let’s see the existed Spring components/beans in application context.

public class ImportComponetsConfigDemo {

	public static void main(String[] args) {
		ApplicationContext ctxt = new AnnotationConfigApplicationContext(ImportComponentsConfig.class);
		String[] components = ctxt.getBeanDefinitionNames();

		for (String bean : components)
			System.out.println(bean);
	}
}

If you run above program, you will see following output and you can notice ExampleComponent in available beans in application context.

importComponentsConfig
com.javabydeveloper.spring.config.importannotation.component.ExampleComponent
componentsTestBean
..... 
......other spring internal beans

4. Spring @Import vs @ComponentScan

@ComponentScan: It tells Spring which packages/components to scan and find using configuration.

@Import: It tells Spring which configurations/components import into another configuration.

4.1. We can achieve same results by using both annotations, but conceptually they use for different purpose. Let’s take look into an example, suppose that we have crocodiles and snakes packages and we configured beans within those using @ComponentScan.

@Configuration
@ComponentScan(basePackages = "com.javabydeveloper.spring.bean.animal.reptiles.snakes")
public class SnakesConfig {
 
}
@Configuration
@ComponentScan(basePackages = "com.javabydeveloper.spring.bean.animal.reptiles.crocodles")
public class CrocodleConfig {

}

Suppose that, now you want another configuration Reptiles that you need both snakes and crocodiles. As both SnakesConfig and CrocodleConfig available, we need to import them into ReptilesConfig instead of scanning them again.

@Configuration
@Import({CrocodleConfig.class, SnakesConfig.class})
public class ReptilesImportConfig {

}

4.2. @ComponentScan annotation has more control on detecting components by using filters/package/classes/annotations.

5. Conclusion

In this tutorial we have learned about Spring @Import annotation and Conceptual difference between @Import vs @ComponentScan. In simple, @ComponentScan is used to detect components in configuration, @Import is used to import one or multiple configurations into another configuration.

6. References

  1. Spring Reference Document
  2. Spring Java Document

Other Related Tutorials:

  1. Spring @Autowired
  2. Spring @Lazy
  3. Spring Boot XML Configuration
  4. Spring Injecting Collection
  5. Spring @Order
  6. Spring @Primary
  7. Spring Component Scanning
  8. Spring @ComponentScan Filter Types

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