设计模式——观察者模式

观察者（发布订阅）模式_发送状态变化通知给所有关注的对象

/**
 * @author maikec
 * @date 2019/5/15
 */
public abstract class AbstractSubject {
    protected Queue<AbstractObserver> observerQueue;

    /**
     * 添加观察者
     * @param observer
     */
    public final void addObserver(AbstractObserver observer){
        if (null == observerQueue){
            ReentrantReadWriteLock.WriteLock writeLock = new ReentrantReadWriteLock().writeLock();
            try {
                if (writeLock.tryLock()){
                    if (null == observerQueue){
                        observerQueue = new PriorityQueue<>(  );
                    }
                }
            }finally {
                writeLock.unlock();
            }
        }

        ReentrantReadWriteLock.WriteLock writeLock = new ReentrantReadWriteLock().writeLock();
        try {
            if (writeLock.tryLock()){
                observerQueue.add( observer );
            }
        }finally {
            writeLock.unlock();
        }
    }

    public final void remove(AbstractObserver observer){
        Assert.notNull( observerQueue,"观察者列表未初始化" );
        Assert.notNull( observer,"入参不能为null" );

        ReentrantReadWriteLock.WriteLock writeLock = new ReentrantReadWriteLock().writeLock();
        try {
            if (writeLock.tryLock()){
                observerQueue.remove( observer );
            }
        }finally {
            writeLock.unlock();
        }
    }
    public final void notifyObservers(){
        observerQueue.forEach( observer -> observer.update( this ) );
    }

    /**
     * 获取主题状态
     * @return
     */
    public abstract String getSubjectStatus();
}

/**
 * @author maikec
 * @date 2019/5/15
 */
public abstract class AbstractObserver {
    /**
     * 观察AbstractSubject状态变化
     * @param subject
     */
    protected abstract void update(AbstractSubject subject);
}

/**
 * @author maikec
 * @date 2019/5/15
 */
public class ConcreteSubject extends AbstractSubject {
    @Setter
    private String status;
    @Override
    public String getSubjectStatus() {
        return status;
    }
}

/**
 * @author maikec
 * @date 2019/5/15
 */
public class ConcreteObserver extends AbstractObserver {
    @Override
    protected void update(AbstractSubject subject) {
        System.out.println( subject.getSubjectStatus() );
    }
}

**
 * @author maikec
 * @date 2019/5/15
 */
public class ObserverDemo {
    public static void main(String[] args) {
        ConcreteSubject concreteSubject = new ConcreteSubject();
        concreteSubject.setStatus( "Active" );

        concreteSubject.addObserver( new ConcreteObserver() );
        concreteSubject.notifyObservers();

        concreteSubject.setStatus( "Down" );
        concreteSubject.notifyObservers();

    }
}
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附录

github.com/maikec/patt… 个人GitHub设计模式案例

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转载于:https://juejin.im/post/5ce8e340f265da1bb96fb8cc