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Spring Java Based Configuration Example

We use @Configuration and @Bean annotations to develop spring application. Note that we haven’t used @Service or @Component annotation in this example. (annotation based configuration)

In this article, we will use @Configuration, @Bean and @Import annotations to demonstrate Spring Java-based configuration example.

Let’s create AppConfiguration and AppConfiguration2 Java classes and annotated with @Configuration annotation. In Java-based configuration auto component scanning not required because Spring beans are created by using factory methods annotated with @Bean annotation.

@Import – much as the element is used within Spring XML files to aid in modularizing configurations, the @Import annotation allows for loading @Bean definitions from another configuration class.

We have created two configuration files and now we will use @Import annotation to import an AppConfiguration2 file into a main AppConfiguration config file.

	@Configuration
	public class AppConfiguration2 {

	@Bean(name="twitterService")
	publicMessageServicetwitterService(){
	return new TwitterService();
	    }

	    @Bean
	publicMessageProcessormessageProcessor(){
	return new MessageProcessorImpl(twitterService());
	    }
	}

Let’s create main app Java-based configuration class.

	@Configuration
	@ComponentScan("com.ducatindia.springframework.di")
	@Import(AppConfiguration2.class)
	publicclassAppConfiguration {

	@Bean(name="emailService")
	publicMessageServiceemailService(){
	returnnewEmailService();
	    }

	@Bean(name="smsService")
	publicMessageServicesmsService(){
	returnnewSMSService();
	    }
	}

Create MessageService interface and it’s multiple implementations.

	public interface MessageService {
	public void sendMsg(String message);
	}

	publicclassSMSServiceimplementsMessageService{
	publicvoidsendMsg(Stringmessage) {
	System.out.println(message);
	    }
	}

	publicclassEmailServiceimplementsMessageService{
	publicvoidsendMsg(Stringmessage) {
	System.out.println(message);
	    }
	}

	publicclassTwitterServiceimplementsMessageService{
	publicvoidsendMsg(Stringmessage) {
	System.out.println(message);
	    }
	}

	publicinterfaceMessageProcessor {
	publicvoidprocessMsg(Stringmessage);
	}
	public class MessageProcessorImpl implements MessageProcessor {
	privateMessageServicemessageService;

	    @Autowired
	publicMessageProcessorImpl(@Qualifier("TwitterService") MessageServicemessageService) {
	this.messageService = messageService;
	    }

	public void processMsg(String message) {
	messageService.sendMsg(message);
	    }
	}

Let’s test this application:

	public class TestApplication {
	public static void main(String[] args) {
	ApplicationContextapplicationContext = new AnnotationConfigApplicationContext(AppConfiguration.class);
	MessageProcessoruserService = applicationContext.getBean(MessageProcessor.class);
	userService.processMsg("Student message sending ");
	    }
	}

Output:

Student message sending

In this example, we used some of the annotations like @Configuration, @Bean, and @Import annotations to demonstrate Spring Java-based configuration. The implementation of this simple Spring Java-based-configuration example can be found in the GitHub project – this is an Eclipse based project, so it should be easy to import and run as it is.

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