<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>GroupId</groupId>
    <artifactId>MessageServiceSpring</artifactId>
    <version>1.0-SNAPSHOT</version>


    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>4.3.9.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-beans</artifactId>
            <version>4.3.9.RELEASE</version>
        </dependency>
    </dependencies>
</project>

package hello;

public interface MessageService {
    String getMessage();
}

package hello;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class MessagePrinter {

    final private MessageService service;

    @Autowired
    public MessagePrinter(MessageService service) {
        this.service = service;
    }

    public void printMessage() {
        System.out.println(this.service.getMessage());
    }
}

package hello;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.*;

@Configuration
@ComponentScan
public class Application {
    // непонятно как работает *** начало
    @Bean
    MessageService mockMessageService() {
        return new MessageService() {
            public String getMessage() {
              return "Hello World!";
            }
        };
    }
    // непонятно как работает *** конец

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

      MessagePrinter printer = context.getBean(MessagePrinter.class);

      printer.printMessage();
  }
}