优雅编程 - SpringEvent

Spring中的事件驱动模型也叫作发布订阅模式,是观察者模式的一个典型的应用 Spring事件驱动模型中存在三个角色: 事件原型、事件发布者、事件监听者.

Spring事件原型

Spring事件定义通过ApplicationEvent,该类继承自Jdk的EventObject; JDK要求所有事件将继承它,并通过source得到事件源, 比如我们的AWT事件体系也是继承自它;

ApplicationEvent规范定义如下:

public abstract class ApplicationEvent extends EventObject {

	/** use serialVersionUID from Spring 1.2 for interoperability */
	private static final long serialVersionUID = 7099057708183571937L;

	/** System time when the event happened */
	private final long timestamp;

	/**
	 * Create a new ApplicationEvent.
	 * @param source the object on which the event initially occurred (never {@code null})
	 */
	public ApplicationEvent(Object source) {
		super(source);
		this.timestamp = System.currentTimeMillis();
	}

	/**
	 * Return the system time in milliseconds when the event happened.
	 */
	public final long getTimestamp() {
		return this.timestamp;
	}
}
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Spring事件发布者

Spring事件发布规范定义在ApplicationEventPublisher中,主要用于事件发布者发布中事件;

ApplicationEventPublisher规范定义如下:

public interface ApplicationEventPublisher {

	/**
	 * Notify all <strong>matching</strong> listeners registered with this
	 * application of an application event. Events may be framework events
	 * (such as RequestHandledEvent) or application-specific events.
	 * @param event the event to publish
	 * @see org.springframework.web.context.support.RequestHandledEvent
	 */
	void publishEvent(ApplicationEvent event);

	/**
	 * Notify all <strong>matching</strong> listeners registered with this
	 * application of an event.
	 * <p>If the specified {@code event} is not an {@link ApplicationEvent},
	 * it is wrapped in a {@link PayloadApplicationEvent}.
	 * @param event the event to publish
	 * @since 4.2
	 * @see PayloadApplicationEvent
	 */
	void publishEvent(Object event);
}
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ApplicationContext接口就集成了ApplicationEventPublisher,如图:

对于ApplicationContext, Spring提供了默认的实现, 在抽象类AbstractApplicationContext中, 常见的 AnnotationConfigWebApplicationContext 、 ClassPathXmlApplicationContext 、 FileSystemXmlApplicationContext 都有继承AbstractApplicationContext的事件行为:

AbstractApplicationContext类中实现代码如下:

/**
 * Publish the given event to all listeners.
 * @param event the event to publish (may be an {@link ApplicationEvent}
 * or a payload object to be turned into a {@link PayloadApplicationEvent})
 * @param eventType the resolved event type, if known
 * @since 4.2
 */
protected void publishEvent(Object event, ResolvableType eventType) {
    Assert.notNull(event, "Event must not be null");
    if (logger.isTraceEnabled()) {
        logger.trace("Publishing event in " + getDisplayName() + ": " + event);
    }

    // Decorate event as an ApplicationEvent if necessary
    ApplicationEvent applicationEvent;
    if (event instanceof ApplicationEvent) {
        applicationEvent = (ApplicationEvent) event;
    }
    else {
        applicationEvent = new PayloadApplicationEvent<Object>(this, event);
        if (eventType == null) {
            eventType = ((PayloadApplicationEvent)applicationEvent).getResolvableType();
        }
    }

    // Multicast right now if possible - or lazily once the multicaster is initialized
    if (this.earlyApplicationEvents != null) {
        this.earlyApplicationEvents.add(applicationEvent);
    }
    else {
        getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType);
    }

    // Publish event via parent context as well...
    if (this.parent != null) {
        if (this.parent instanceof AbstractApplicationContext) {
            ((AbstractApplicationContext) this.parent).publishEvent(event, eventType);
        }
        else {
            this.parent.publishEvent(event);
        }
    }
}
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在这个方法中,我们看到了一getApplicationEventMulticaster();ApplicationEventMulticaster.属于事件广播器,它的作用是把ApplicationContext发布的Event广播给所有的监听器.

Spring事件监听者

Spring中ApplicationListener是事件监控者规范的定义, 定义内容如下:

public interface ApplicationListener<E extends ApplicationEvent> extends EventListener {
	/**
	 * Handle an application event.
	 * @param event the event to respond to
	 */
	void onApplicationEvent(E event);
}
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ApplicationListener继承自jdk的EventListener,所有的监听器都要实现这个接口,这个接口只有一个onApplicationEvent()方法,该方法接受一个ApplicationEvent或其子类对象作为参数,在方法体中,可以通过不同对Event类的判断来进行相应的处理.当事件触发时所有的监听器都会收到消息,如果你需要对监听器的接收顺序有要求,可以实现该接口的一个子接口SmartApplicationListener,通过这个接口可以指定监听器接收事件的顺序.

SmartApplicationListener的接口集成关系如下:

SpringEvent 事件应用示例

事件定义

public class PlanAllocatePubEvent extends ApplicationEvent {

    public PlanAllocatePubEvent(Long allocateId) {
        super(allocateId);
    }
}
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事件发布

@Component
public class PlanAllocatePubPublisher {

    private static final Logger LOG = LoggerFactory.getLogger(PlanAllocatePubPublisher.class);

    @Autowired
    private ApplicationEventPublisher applicationEventPublisher;

    public void publishEvent(long allocateId){
        LOG.info("[事件发布] 数据创建, 编号:" + allocateId);
        PlanAllocatePubEvent event = new PlanAllocatePubEvent(allocateId);
        applicationEventPublisher.publishEvent(event);
    }
}
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事件监听(无序)

同步事件处理

@Component
public class SyncPlanAllocatePubListener implements ApplicationListener<PlanAllocatePubEvent>{

    private static final Logger LOG = LoggerFactory.getLogger(SyncPlanAllocatePubListener.class);

    @Override
    public void onApplicationEvent(PlanAllocatePubEvent planAllocatePubEvent) {
        LOG.info("[同步][事件监听][开始]数据创建, 数据编号:" + planAllocatePubEvent.getSource());
        doSomething();
        LOG.info("[同步][事件监听][结束]数据创建, 数据编号:" + planAllocatePubEvent.getSource());
    }

    public void doSomething(){
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            LOG.error(e.getLocalizedMessage(), e);
        }
    }

}
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异步事件处理

@Component
@EnableAsync
public class AsynPlanAllocatePubListener implements ApplicationListener<PlanAllocatePubEvent> {

    private static final Logger LOG = LoggerFactory.getLogger(AsynPlanAllocatePubListener.class);

    @Async
    @Override
    public void onApplicationEvent(PlanAllocatePubEvent planAllocatePubEvent) {
        LOG.info("[异步][事件监听][开始]数据创建, 数据编号:" + planAllocatePubEvent.getSource());
        doSomething();
        LOG.info("[异步][事件监听][结束]数据创建, 数据编号:" + planAllocatePubEvent.getSource());
    }

    public void doSomething(){
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            LOG.error(e.getLocalizedMessage(), e);
        }
    }

}
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事件监听(有序)

示例代码: 事件监听逻辑1

@Component
public class Order1PlanAllocatePubListener implements SmartApplicationListener {

    private static final Logger LOG = LoggerFactory.getLogger(Order1PlanAllocatePubListener.class);

    /**
     * supportsEventType用于指定支持的事件类型，只有支持的才调用onApplicationEvent
     * @param eventType
     * @return
     */
    @Override
    public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) {
        return eventType == PlanAllocatePubEvent.class;
    }

    /**
     * supportsSourceType支持的目标类型，只有支持的才调用onApplicationEvent
     * @param sourceType
     * @return
     */
    @Override
    public boolean supportsSourceType(Class<?> sourceType) {
        return sourceType == Long.class;
    }

    @Override
    public void onApplicationEvent(ApplicationEvent event) {
        LOG.info("[有序事件][事件监听][Order:1]数据创建, 编号:" + event.getSource());
        doSomething();
    }

    /**
     * 优先级顺序，越小优先级越高
     * @return
     */
    @Override
    public int getOrder() {
        return 1;
    }

    public void doSomething(){
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            LOG.error(e.getLocalizedMessage(), e);
        }
    }
}
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示例代码: 事件监听逻辑2

@Component
public class Order2PlanAllocatePubListener implements SmartApplicationListener{

    private static final Logger LOG =  LoggerFactory.getLogger(Order2PlanAllocatePubListener.class);

    /**
     * supportsEventType用于指定支持的事件类型，只有支持的才调用onApplicationEvent
     * @param eventType
     * @return
     */
    @Override
    public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) {
        return eventType == PlanAllocatePubEvent.class;
    }

    /**
     * supportsSourceType支持的目标类型，只有支持的才调用onApplicationEvent
     * @param sourceType
     * @return
     */
    @Override
    public boolean supportsSourceType(Class<?> sourceType) {
        return sourceType == Long.class;
    }

    @Override
    public void onApplicationEvent(ApplicationEvent event) {
        LOG.info("[有序事件][事件监听][Order:2]数据创建, 编号:" + event.getSource());
        doSomething();
    }

    /**
     * 优先级顺序，越小优先级越高
     * @return
     */
    @Override
    public int getOrder() {
        return 2;
    }

    public void doSomething(){
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            LOG.error(e.getLocalizedMessage(), e);
        }
    }
}
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测试事件

@Controller
@RequestMapping(value = "/api/event")
public class ApiPluginEventController {

    @Autowired
    private PlanAllocatePubPublisher planAllocatePubPublisher;

    @ResponseBody
    @GetMapping(value = "/publish")
    public Map pubEvent() throws Exception {
        for(int i=1; i<5; i++){
            planAllocatePubPublisher.publishEvent(i);
        }
        return ImmutableMap.builder().put("message", "ok").build();
    }
}
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异步事件执行结果

INFO:2017-09-11 20:14:08.799[publishEvent] [事件发布] 数据创建, 数据编号:1 
INFO:2017-09-11 20:14:08.803[publishEvent] [事件发布] 数据创建, 数据编号:2 
INFO:2017-09-11 20:14:08.803[onApplicationEvent] [异步][事件监听][开始]数据创建, 数据编号:1 
INFO:2017-09-11 20:14:08.804[publishEvent] [事件发布] 数据创建, 数据编号:3 
INFO:2017-09-11 20:14:08.804[onApplicationEvent] [异步][事件监听][开始]数据创建, 数据编号:2 
INFO:2017-09-11 20:14:08.805[onApplicationEvent] [异步][事件监听][开始]数据创建, 数据编号:3 
INFO:2017-09-11 20:14:08.804[publishEvent] [事件发布] 数据创建, 数据编号4 
INFO:2017-09-11 20:14:08.805[onApplicationEvent] [异步][事件监听][开始]数据创建, 数据编号:4 
INFO:2017-09-11 20:14:11.807[onApplicationEvent] [异步][事件监听][结束]数据创建, 数据编号:1 
INFO:2017-09-11 20:14:11.807[onApplicationEvent] [异步][事件监听][结束]数据创建, 数据编号:2 
INFO:2017-09-11 20:14:11.807[onApplicationEvent] [异步][事件监听][结束]数据创建, 数据编号:3 
INFO:2017-09-11 20:14:11.809[onApplicationEvent] [异步][事件监听][结束]数据创建, 数据编号:4 
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同步事件执行结果

INFO:2017-09-11 20:17:07.470[publishEvent] [事件发布] 数据创建, 数据编号:1 
INFO:2017-09-11 20:17:07.473[onApplicationEvent] [同步][事件监听][开始]数据创建, 数据编号:1 
INFO:2017-09-11 20:17:09.476[onApplicationEvent] [同步][事件监听][结束]数据创建, 数据编号:1 
INFO:2017-09-11 20:17:09.477[publishEvent] [事件发布] 数据创建, 数据编号:2 
INFO:2017-09-11 20:17:09.478[onApplicationEvent] [同步][事件监听][开始]数据创建, 数据编号:2 
INFO:2017-09-11 20:17:11.481[onApplicationEvent] [同步][事件监听][结束]数据创建, 数据编号:2 
INFO:2017-09-11 20:17:11.481[publishEvent] [事件发布] 数据创建, 数据编号:3 
INFO:2017-09-11 20:17:11.482[onApplicationEvent] [同步][事件监听][开始]数据创建, 数据编号:3 
INFO:2017-09-11 20:17:13.486[onApplicationEvent] [同步][事件监听][结束]数据创建, 数据编号:3 
INFO:2017-09-11 20:17:13.487[publishEvent] [事件发布] 数据创建, 数据编号:4 
INFO:2017-09-11 20:17:13.487[onApplicationEvent] [同步][事件监听][开始]数据创建, 数据编号:4 
INFO:2017-09-11 20:17:15.492[onApplicationEvent] [同步][事件监听][结束]数据创建, 数据编号:4 
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有序事件执行结果

INFO:2017-09-11 20:33:12.139[publishEvent] [事件发布] 数据创建, 编号:1 
INFO:2017-09-11 20:33:12.140[onApplicationEvent] [有序事件][事件监听][Order:1]数据创建, 编号:1 
INFO:2017-09-11 20:33:15.145[onApplicationEvent] [有序事件][事件监听][Order:2]数据创建, 编号:1 
INFO:2017-09-11 20:33:18.146[publishEvent] [事件发布] 数据创建, 编号:2 
INFO:2017-09-11 20:33:18.147[onApplicationEvent] [有序事件][事件监听][Order:1]数据创建, 编号:2 
INFO:2017-09-11 20:33:21.151[onApplicationEvent] [有序事件][事件监听][Order:2]数据创建, 编号:2 
INFO:2017-09-11 20:33:24.156[publishEvent] [事件发布] 数据创建, 编号:3 
INFO:2017-09-11 20:33:24.157[onApplicationEvent] [有序事件][事件监听][Order:1]数据创建, 编号:3 
INFO:2017-09-11 20:33:27.162[onApplicationEvent] [有序事件][事件监听][Order:2]数据创建, 编号:3 
INFO:2017-09-11 20:33:30.167[publishEvent] [事件发布] 数据创建, 编号:4 
INFO:2017-09-11 20:33:30.168[onApplicationEvent] [有序事件][事件监听][Order:1]数据创建, 编号:4 
INFO:2017-09-11 20:33:33.171[onApplicationEvent] [有序事件][事件监听][Order:2]数据创建, 编号:4 
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注解事件监听

Spring4.2开始提供了@EventListener注解，使得监听器不再需要实现ApplicationListener接口，只需要在监听方法上加上该注解即可，方法不一定叫onApplicationEvent，但有且只能有一个参数，指定监听的事件类型. 上面示例中的有序事件监听逻辑可以使用注解方式实现:

@Component
public class PlanAllocatePubHandler {

    private static final Logger LOG = LoggerFactory.getLogger(PlanAllocatePubHandler.class);

    /**
     * 基于注解的事件监听
     * @param planAllocatePubEvent
     */
    @EventListener
    @Order(1)
    public void annoEnvListener1(PlanAllocatePubEvent planAllocatePubEvent) {
        LOG.info("[注解事件监听][Order:1]数据创建, 编号:" + planAllocatePubEvent.getSource());
        doSomething();
    }

    /**
     * 基于注解的事件监听
     * @param planAllocatePubEvent
     */
    @EventListener
    @Order(2)
    public void annoEnvListener2(PlanAllocatePubEvent planAllocatePubEvent) {
        LOG.info("[注解事件监听][Order:2]数据创建, 编号:" + planAllocatePubEvent.getSource());
        doSomething();
    }

    public void doSomething(){
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            LOG.error(e.getLocalizedMessage(), e);
        }
    }
}
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注解事件监听执行结果

INFO:2017-09-11 20:57:00.167[publishEvent] [事件发布] 数据创建, 编号:1 
INFO:2017-09-11 20:57:00.168[annoEnvListener1] [注解事件监听][Order:1]数据创建, 编号:1 
INFO:2017-09-11 20:57:03.169[annoEnvListener2] [注解事件监听][Order:2]数据创建, 编号:1 
INFO:2017-09-11 20:57:06.175[publishEvent] [事件发布] 数据创建, 编号:2 
INFO:2017-09-11 20:57:06.176[annoEnvListener1] [注解事件监听][Order:1]数据创建, 编号:2 
INFO:2017-09-11 20:57:09.180[annoEnvListener2] [注解事件监听][Order:2]数据创建, 编号:2 
INFO:2017-09-11 20:57:12.184[publishEvent] [事件发布] 数据创建, 编号:3 
INFO:2017-09-11 20:57:12.185[annoEnvListener1] [注解事件监听][Order:1]数据创建, 编号:3 
INFO:2017-09-11 20:57:15.191[annoEnvListener2] [注解事件监听][Order:2]数据创建, 编号:3 
INFO:2017-09-11 20:57:18.195[publishEvent] [事件发布] 数据创建, 编号:4 
INFO:2017-09-11 20:57:18.196[annoEnvListener1] [注解事件监听][Order:1]数据创建, 编号:4 
INFO:2017-09-11 20:57:21.198[annoEnvListener2] [注解事件监听][Order:2]数据创建, 编号:4 
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