Dependency Pull Demo : Dependency Injection « Spring « Java Tutorial

1. Java Tutorial
2. Spring
3. Dependency Injection

File: context.properties

source.(class)=SimpleMessageData
destination.(class)=StdoutMessageReporter
service.(class)=DefaultMessageService
service.source(ref)=source
service.destination(ref)=destination

File: Main.java

import org.springframework.beans.factory.support.BeanDefinitionReader;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.support.PropertiesBeanDefinitionReader;
import org.springframework.core.io.ClassPathResource;
import org.springframework.util.Assert;

public class Main {

  public static void main(String[] args) throws Exception {
    DefaultListableBeanFactory bf = new DefaultListableBeanFactory();
    BeanDefinitionReader reader = new PropertiesBeanDefinitionReader(bf);
    reader.loadBeanDefinitions(new ClassPathResource("context.properties"));

    MessageService service = (MessageService) bf.getBean("service");
    service.execute();

  }
}

class DependantComponent {
  private MessageService service;

  public DependantComponent(MessageService service) {
    Assert.notNull(service, "The 'service' argument must not be null.");
    this.service = service;
  }

  public void run() {
    this.service.execute();
  }
}

interface MessageService {

  void execute();

}

class DefaultMessageService implements MessageService {
  private MessageData source;

  private MessageReporter destination;

  public void execute() {
    this.destination.write(this.source.getMessage());
  }

  public void setSource(MessageData source) {
    this.source = source;
  }

  public void setDestination(MessageReporter destination) {
    this.destination = destination;
  }
}

interface MessageReporter {

  void write(String message);

}

interface MessageData {

  String getMessage();

}

class StdoutMessageReporter implements MessageReporter {

  public void write(String message) {
    System.out.println(message);
  }
}

class SimpleMessageData implements MessageData {
  private final String message;

  public SimpleMessageData() {
    this("Hello, world");
  }

  public SimpleMessageData(String message) {
    this.message = message;
  }

  public String getMessage() {
    return this.message;
  }
}

28.8.Dependency Injection
	28.8.1.	Dependency Pull Demo
	28.8.2.	dependency check Demo
	28.8.3.	Contextualized Dependency Lookup Demo
	28.8.4.	Spring bean dependency Demo
	28.8.5.	Setter Dependency Injection Demo
	28.8.6.	Dependency Injection Demo