spring事件（一）--内置事件

一、简介

spring框架是java开发中常用的，通常我们需要在spring的某些事件发生时，做某些操作。

在此介绍spring的内置事件，以父抽象类ApplicationContextEvent下的四个子事件类为主。

类图如下：

二、事件类

1、ApplicationContextEvent

是spring内置事件的父抽象类，构造方法传入spring的context容器，同时也有获取spring的context容器的方法。

源码如下：

/** * Base class for events raised for an {@code ApplicationContext}. * * @author Juergen Hoeller * @since 2.5 */@SuppressWarnings("serial")public abstract class ApplicationContextEvent extends ApplicationEvent {   /**    * Create a new ContextStartedEvent.    * @param source the {@code ApplicationContext} that the event is raised for    * (must not be {@code null})    */   public ApplicationContextEvent(ApplicationContext source) {      super(source);   }   /**    * Get the {@code ApplicationContext} that the event was raised for.    */   public final ApplicationContext getApplicationContext() {      return (ApplicationContext) getSource();   }}

2、ContextRefreshedEvent

当spring容器初始化或刷新时，会触发此事件。此事件在开发中常用，用于在spring容器启动时，导入自定义的bean实例到spring容器中。

源码如下：

/** * Event raised when an {@code ApplicationContext} gets initialized or refreshed. * * @author Juergen Hoeller * @since 04.03.2003 * @see ContextClosedEvent */@SuppressWarnings("serial")public class ContextRefreshedEvent extends ApplicationContextEvent {   /**    * Create a new ContextRefreshedEvent.    * @param source the {@code ApplicationContext} that has been initialized    * or refreshed (must not be {@code null})    */   public ContextRefreshedEvent(ApplicationContext source) {      super(source);   }}

3、ContextStartedEvent

当spring启动时，或者说是context调用start()方法时，会触发此事件。

源码如下：

/** * Event raised when an {@code ApplicationContext} gets started. * * @author Mark Fisher * @author Juergen Hoeller * @since 2.5 * @see ContextStoppedEvent */@SuppressWarnings("serial")public class ContextStartedEvent extends ApplicationContextEvent {   /**    * Create a new ContextStartedEvent.    * @param source the {@code ApplicationContext} that has been started    * (must not be {@code null})    */   public ContextStartedEvent(ApplicationContext source) {      super(source);   }}

4、ContextStoppedEvent

当spring停止时，或者说context调用stop()方法时，会触发此事件。

源码如下：

/** * Event raised when an {@code ApplicationContext} gets stopped. * * @author Mark Fisher * @author Juergen Hoeller * @since 2.5 * @see ContextStartedEvent */@SuppressWarnings("serial")public class ContextStoppedEvent extends ApplicationContextEvent {   /**    * Create a new ContextStoppedEvent.    * @param source the {@code ApplicationContext} that has been stopped    * (must not be {@code null})    */   public ContextStoppedEvent(ApplicationContext source) {      super(source);   }}

5、ContextClosedEvent

当spring关闭时，或者说context调用close()方法时，会触发此事件。

源码如下：

/** * Event raised when an {@code ApplicationContext} gets closed. * * @author Juergen Hoeller * @since 12.08.2003 * @see ContextRefreshedEvent */@SuppressWarnings("serial")public class ContextClosedEvent extends ApplicationContextEvent {   /**    * Creates a new ContextClosedEvent.    * @param source the {@code ApplicationContext} that has been closed    * (must not be {@code null})    */   public ContextClosedEvent(ApplicationContext source) {      super(source);   }}

三、监听类

在spring中，我们通常实现接口ApplicationListener<Event>来对事件进行监听，泛型传入事件的类型。

在接口内的方法onApplicationEvent中实现监听到事件时需处理的逻辑。

ApplicationListener接口的源码如下：

/** * Interface to be implemented by application event listeners. * Based on the standard {@code java.util.EventListener} interface * for the Observer design pattern. * * <p>As of Spring 3.0, an ApplicationListener can generically declare the event type * that it is interested in. When registered with a Spring ApplicationContext, events * will be filtered accordingly, with the listener getting invoked for matching event * objects only. * * @author Rod Johnson * @author Juergen Hoeller * @param <E> the specific ApplicationEvent subclass to listen to * @see org.springframework.context.event.ApplicationEventMulticaster */public interface ApplicationListener<E extends ApplicationEvent> extends EventListener {   /**    * Handle an application event.    * @param event the event to respond to    */   void onApplicationEvent(E event);}

四、代码实例

代码中，我们可以直接实现不带泛型的接口ApplicationListener，在代码中对不同事件做不同处理，如：

@Componentpublic class SpringContextEventDemo  implements ApplicationListener {    public void onApplicationEvent(ApplicationEvent event) {        if(event instanceof ContextRefreshedEvent){            System.out.println("ContextRefreshedEvent happen");        }else if(event instanceof ContextStartedEvent){            System.out.println("ContextStartedEvent happen");        }else if(event instanceof ContextStoppedEvent){            System.out.println("ContextStoppedEvent happen");        }else if(event instanceof ContextClosedEvent){            System.out.println("ContextClosedEvent happen");        }    }}

也可直接监听特定事件，即实现带泛型接口的ApplicationListener，在此以监听ContextRefreshedEvent事件为例。

1、监听类

@Componentpublic class SpringContextRefreshedEventDemo implements ApplicationListener<ContextRefreshedEvent> {    public void onApplicationEvent(ContextRefreshedEvent contextRefreshedEvent) {        ApplicationContext ctx = contextRefreshedEvent.getApplicationContext();        System.out.println("ContextRefreshedEvent happen");    }}

2、测试类

public class SpringSelfEventMain {    public static void main(String[] args) {        AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(SpringConfig.class);//        ctx.start();  //ContextStartedEvent事件发生//        ctx.stop();   //ContextStoppedEvent事件发生//        ctx.close();  //ContextClosedEvent事件发生    }}

运行结果（在spring容器启动时，触发ContextRefreshedEvent事件，执行监听逻辑）：

ContextRefreshedEvent happen