Reshma Bidikar

In this article, I will be demonstrating how Spring Java-Based Configuration works. I will be using Eclipse and Maven. In order to get a basic introduction to Spring, you can check out this article. In order to understand how to configure a standalone Spring application using XML configuration, you can refer to this article.

Project Set-up

Step 1 - Create a new Maven Project in Eclipse. You can refer to this article on how to create a Maven project in Eclipse.

Step 2 - Add Spring dependencies to the maven pom file. You can add the following:

<dependencies>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-core</artifactId>
      <version>5.2.2.RELEASE</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>5.2.2.RELEASE</version>
    </dependency>
  </dependencies>

Creating Beans

Create the following bean classes:

MessageDAO:

public class MessageDAO {
  
  public String getMessage() {
    return "Hello World";
  }

}

MessageDAO is a simple class that has only one method getMessage()This returns a String value.

MessageService:

public class MessageService {
  
  private MessageDAO messageDAO;

  public void printMessage() {
    String message = messageDAO.getMessage();
    System.out.println(message);
  }

  public MessageDAO getMessageDAO() {
    return messageDAO;
  }

  public void setMessageDAO(MessageDAO messageDAO) {
    this.messageDAO = messageDAO;
  }

}

MessageService has a method printMessage. It uses the MessageDAOto obtain the message and prints it. It has a private field corresponding to MessageDAOand getter/setter methods for it.

Configuration Class

Create a class called MyConfiguration as follows:

@Configuration
public class MyConfiguration {
  @Bean
  public MessageDAO messageDAO() {
    MessageDAO bean = new MessageDAO();
    return bean;

  }

  @Bean
  public MessageService messageService() {
    MessageService bean = new MessageService();
    bean.setMessageDAO(messageDAO());
    return bean;
  }

}

The MyConfigurationclass has the @Configurationannotation. This indicates that this class contains the configuration metadata. This has two methods marked with the @Beanannotation. The names of the method are the same as the bean names. Spring uses these methods to create the beans at startup.

Writing Main Code

Create a class Main.java with the following code:

	public static void main(String args[]) {
		AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(
				MyConfiguration.class);
		MessageService messageService = applicationContext.getBean("messageService", MessageService.class);
		
		messageService.printMessage();
	}

The org.springframework.context..ApplicationContextinterface represents the Spring Container. This code first creates a AnnotationConfigApplicationContextinstance which is an implementation of the ApplicationContextinterface. There are several other implementations too. The AnnotationConfigApplicationContext is used in case of Java/annotation configuration.

ApplicationContexthas a method getBean. The code invokes this method in order to obtain theMessageService. The code then invokes the printMessagemethod.

So on execution, this code prints the following output:

Hello World

Further Learning

• Spring MasterClass
• Spring Tutorial For Beginners
• Step by Step Spring MVC Tutorial
• Spring Framework in Easy Steps

Conclusion

So in this article, we saw a Spring Java-Based configuration example. We saw how to configure a standalone Spring application via a Java class configuration. We used Eclipse and Maven in this example.