[享学Netflix] 三、Apache Commons Configuration2.x全新的事件-监听机制

public class Event extends EventObject {

	// root event。所以事件类型都直接/间接的继承自它
	// 如果你监听的是这种事件类型：那就是监听所有的事件
	public static final EventType<Event> ANY = new EventType<>(null, "ANY");

	// 唯一构造器  source和EventType是必须的，确定了你发送的事件源 和类型
	// 比如对Person的新增。person是事件源，新增是事件类型
	public Event(final Object source, final EventType<? extends Event> evType) { ... }
	
}

public class ConfigurationEvent extends Event {

	// 该事件源内置的事件类型们，是public的哦
	public static final EventType<ConfigurationEvent> ANY = new EventType<>(Event.ANY, "CONFIGURATION_UPDATE");
	public static final EventType<ConfigurationEvent> ADD_PROPERTY = new EventType<>(ANY, "ADD_PROPERTY");
	... // 增删改等非常多的操作
    private final String propertyName;
    private final Object propertyValue;
    private final boolean beforeUpdate;
    ...
}

public class ConfigurationEvent extends Event {

    public static final EventType<ConfigurationEvent> ANY = new EventType<>(Event.ANY, "CONFIGURATION_UPDATE");
    public static final EventType<ConfigurationEvent> ADD_PROPERTY = new EventType<>(ANY, "ADD_PROPERTY");
    ... // 省略其它事件类型
    
    private final String propertyName;
    private final Object propertyValue;
    private final boolean beforeUpdate;
	...
}

public class ReloadingEvent extends Event {

	// 注意：它仅有这一个事件类型，木有子类型
    public static final EventType<ReloadingEvent> ANY = new EventType<>(Event.ANY, "RELOAD");
    
    // reloading时发送的额外数据，没有可为null
    private final Object data;

	// 小细节：从这个方法可以得出结论
	// 发送这个事件的事件源：一定是ReloadingController
    public ReloadingController getController() {
        return (ReloadingController) getSource();
    }
}

public class ConfigurationBuilderEvent extends Event {

    public static final EventType<ConfigurationBuilderEvent> ANY = new EventType<>(Event.ANY, "BUILDER");
	
	// 在BasicConfigurationBuilder#resetResult()方法被调用的时候，此事件发出
    public static final EventType<ConfigurationBuilderEvent> RESET = new EventType<>(ANY, "RESET");
	// ConfigurationBuilder#getConfiguration()被调用时候，获取时。发送这个事件
	// 当时请注意：这这是发起了request，但不一定get成功了（中途可能抛出异常嘛）
    public static final EventType<ConfigurationBuilderEvent> CONFIGURATION_REQUEST = new EventType<>(ANY, "CONFIGURATION_REQUEST");


	// 同样的，这个事件源必须是`ConfigurationBuilder`
    @Override
    public ConfigurationBuilder<?> getSource() {
        return (ConfigurationBuilder<?>) super.getSource();
    }
}

public class ConfigurationBuilderResultCreatedEvent extends ConfigurationBuilderEvent {

	// 它表示Result获取**成功**后，发送的事件
    public static final EventType<ConfigurationBuilderResultCreatedEvent> RESULT_CREATED = new EventType<>(ANY, "RESULT_CREATED");

	// 提供对配置对象的访问，毕竟发送此事件代表肯定创建成功了嘛~
	// 绝大部分情况是Configuration
	private final ImmutableConfiguration configuration;
}

public class EventType<T extends Event> implements Serializable {

	private final EventType<? super T> superType;
	private final String name;
	
	... // 省略构造器

	// 获取到该类型所有的父类型（递归调用到顶层）
	public static Set<EventType<?>> fetchSuperEventTypes(final EventType<?> eventType) { ... }
	// derivedType是否是baseType的子类型（递归去比较）
	public static boolean isInstanceOf(final EventType<?> derivedType, final EventType<?> baseType) { ... }
}

public interface EventListener<T extends Event> {
	void onEvent(T event);
}

// 说明：它监听的是所有事件哦~~~~
final class ReloadingBuilderSupportListener implements EventListener<Event> {
	private final BasicConfigurationBuilder<?> builder;
	private final ReloadingController reloadingController;
	... // 省略构造器赋值

	// 当监听的事件是：RESULT_CREATED，也就是Configuration被成功创建return出去后，给重置其ReloadingState
	// 也就是说保证获取出去的对象仍可以热加载..

	// 而如果是其它事件，resetResult() -> result =null并且发出RESET事件
    @Override
    public void onEvent(final Event event) {
        if (ConfigurationBuilderResultCreatedEvent.RESULT_CREATED.equals(event.getEventType())) {
            reloadingController.resetReloadingState();
        } else {
            builder.resetResult();
        }
    }

	// =======同时它还提供一个静态方法，方便你绑定======
    public static ReloadingBuilderSupportListener connect(
            final BasicConfigurationBuilder<?> configBuilder,
            final ReloadingController controller) {
            
		final ReloadingBuilderSupportListener listener = new ReloadingBuilderSupportListener(configBuilder, controller);
		// 把该时间绑定在ReloadingController上
		// 说明：ReloadingController它自己是个EventSource哦，所以可以监听它
		// 并且它可以发出ReloadingEvent事件出来。所以发现，当发出ReloadingEvent出来时，触发本监听器的resetResult操作
		controller.addEventListener(ReloadingEvent.ANY, listener);

		// 给builder监听上RESULT_CREATED这个事件，当RESULT_CREATED到达此监听器时候会清空Result
		configBuilder.installEventListener( ConfigurationBuilderResultCreatedEvent.RESULT_CREATED, listener);

		return listener;
	}
}

// 为注册监听器时提供数据
public final class EventListenerRegistrationData<T extends Event> {
	private final EventType<T> eventType;
	private final EventListener<? super T> listener;
}

public class EventListenerList {
	private final List<EventListenerRegistrationData<?>> listeners;
	// 可以看到对它的增删改都是线程安全的
    public EventListenerList() {
        listeners = new CopyOnWriteArrayList<>();
    }
	... //addEventListener/removeEventListener/fire/getEventListeners


	// 拿到监听此事件类型（以及其所有子事件类型）所有的监听器们
	public <T extends Event> List<EventListenerRegistrationData<? extends T>> getRegistrationsForSuperType(EventType<T> eventType) { ... }
	...
}

@Test
public void fun100() throws ConfigurationException {
    Configurations configs = new Configurations();
    PropertiesConfiguration config = configs.properties("1.properties");

    // 监听ADD_PROPERTY添加属性事件
    config.addEventListener(ConfigurationEvent.ADD_PROPERTY, event -> {
        if (!event.isBeforeUpdate()) {
            System.out.printf("成功添加属性：%s = %s", event.getPropertyName(), event.getPropertyValue());
        }
    });

    config.addProperty("name","YourBatman");
}

成功添加属性：name = YourBatman