행위패턴 : Observer 패턴

분류 : 행위패턴(Behavioral Patterns)

정의 :

observer(옵저버, 관찰자)라고하는 종속성 목록을 관리하고, 목록에 속한 객체들에게 상태 변화를 통지하는 객체를 이용하는 패턴.

용도 :

분산 이벤트 핸들링 시스템에서 주로 사용됨.

MVC(Model-View-Controller) 아키텍처 패턴에서 중용한 역할을 함.

소스

import java.util.Observable;          //Observable is here
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
 
public class EventSource extends Observable implements Runnable {
    public void run() {
        try {
            final InputStreamReader isr = new InputStreamReader(System.in);
            final BufferedReader br = new BufferedReader(isr);
            while (true) {
                String response = br.readLine();
                setChanged();
                notifyObservers(response);
            }
        }
        catch (IOException e) {
            e.printStackTrace();
        }
    }
}


import java.util.Observable;
import java.util.Observer;  /* this is Event Handler */
 
public class ResponseHandler implements Observer {
    private String resp;
    public void update(Observable obj, Object arg) {
        if (arg instanceof String) {
            resp = (String) arg;
            System.out.println("\nReceived Response: " + resp );
        }
    }
}

public class MyApp {
    public static void main(String[] args) {
        System.out.println("Enter Text >");
 
        // create an event source - reads from stdin
        final EventSource eventSource = new EventSource();
 
        // create an observer
        final ResponseHandler responseHandler = new ResponseHandler();
 
        // subscribe the observer to the event source
        eventSource.addObserver(responseHandler);
 
        // starts the event thread
        Thread thread = new Thread(eventSource);
        thread.start();
    }
}

참고자료

http://en.wikipedia.org/wiki/Observer_pattern