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
    
      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();    }}复制代码
    

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