Java/Spring/Decouple

Closed Coupled

       
File: Main.java
import java.io.PrintStream;
public class Main {
  public static void main(String[] a) {
    MessageData source = new MessageData("Hello, world");
    MessageReporter destination = new MessageReporter();
    destination.write(System.out, source.getMessage());
  }
}
final class MessageData {
  private final String message;
  public MessageData(String message) {
    this.message = message;
  }
  public String getMessage() {
    return message;
  }
}
class MessageReporter {
  public void write(PrintStream out, String message) {
    out.println(message);
  }
}

Decouple With Interface

       
File: Main.java

public class Main {
  public static void main(String[] a) {
    MessageData source = new SimpleMessageData("Hello, world");
    MessageReporter destination = new StdoutMessageReporter();
    destination.write(source.getMessage());
  }
}
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;
  }
}

Spring Prototype

       
File: Main.java
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Main {
  public static void main(String[] z) {
    ApplicationContext context = new ClassPathXmlApplicationContext("context.xml", Main.class);
    SpringPrototypeClient client = (SpringPrototypeClient) context.getBean("prototypeClient");
    client.run();
  }
}
class SpringPrototypeClient {
  private Message message1;
  private Message message2;
  public void run() {
      System.out.println("Message1 " + this.message1.toString());
      System.out.println("Message2 " + this.message2.toString());
      System.out.println("Messages == " + (this.message1 == this.message2));
  }
  public void setMessage1(Message message1) {
      this.message1 = message1;
  }
  public void setMessage2(Message message2) {
      this.message2 = message2;
  }
}
abstract class Message {
  public Message makeCopy() {
    try {
      return this.getClass().newInstance();
    } catch (InstantiationException e) {
      return null;
    } catch (IllegalAccessException e) {
      return null;
    }
  }
}
class EmailMessage extends Message {
  @Override
  public String toString() {
    return "EmailMessage";
  }
}

File: context.xml
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN"
"http://www.springframework.org/dtd/spring-beans.dtd">
<beans>
    <bean id="prototypeClient"
          class="SpringPrototypeClient">
        <property name="message1" ref="message"/>
        <property name="message2" ref="message"/>
    </bean>
    <bean id="message" class="EmailMessage" singleton="false"/>
</beans>

Spring Style Decouple

       
File: helloworld-context.properties
source.(class)=SimpleMessageData
destination.(class)=StdoutMessageReporter

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;
public class Main {
  public static void main(String[] a) {
    DefaultListableBeanFactory bf = new DefaultListableBeanFactory();
    BeanDefinitionReader reader = new PropertiesBeanDefinitionReader(bf);
    reader.loadBeanDefinitions(new ClassPathResource("helloworld-context.properties"));
    MessageData source = (MessageData) bf.getBean("source");
    MessageReporter destination = (MessageReporter) bf.getBean("destination");
    destination.write(source.getMessage());
  }
}
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;
  }
}