Spring中的事件处理
ApplicationContext 是Spring的核心模块，管理着Beans完整的生命周期。当加载Bean时，ApplicationContext会发布特定类型的事件。
eg:当Context启动时ContextStartEvent被发布，当关闭时，ContextStoppedEvent被发布。
ApplicationContext事件处理被ApplicationEvent类和ApplicationListener接口提供。因此，实现了ApplicationListener的bean，每次ApplicationContext发布ApplicationEvent时，Bean将会被通知。
Spring内建事件ContextRefreshedEvent : 当ApplicationContext被初始化或者刷新时被发布。也可以通过调用ConfigurableApplicationContext接口的refresh()函数发起。
ContextStartedEvent : 当Application使用ConfigurableApplicationContext的start()方法启动时被发布。您可以轮询您的数据库，也可以在收到此事件后重新启动任何已停止的应用程序。
ContextStoppedEvent : 当ApplicationContext在ConfigurableApplicationContext接口上使用stop()方法停止时，就会发布这个事件。你可以在收到这个活动后做家务。
ContextClosedEvent : 当使用ConfigurableApplicationContext接口上的close()方法关闭ApplicationContext时，将发布此事件。一个封闭的环境到达了生命的终点;不能刷新或重新启动。
RequestHandledEvent : 这是一个特定于web的事件，它告诉所有bean HTTP请求已经得到了服务。
Spring的事件处理是单线程的，因此如果发布了一个事件，直到并且除非所有接收者都得到消息，否则进程将被阻塞，线程将不会继续。因此，如果要使用事件处理，那么在设计应用程序时应该小心。
监听Context事件要想监听一个context事件，bean需要实现仅有一个方法onApplicationEvent()的ApplicationListener接口
ExampleHelloWorld.java
public class HelloWorld { private String message; public void setMessage(String message){ this.message = message; } public void getMessage(){ System.out.println("Your Message : " + message); } }CStartEventHandler.java
public class CStartEventHandler implements ApplicationListener<ContextStartedEvent>{ public void onApplicationEvent(ContextStartedEvent event) { System.out.println("ContextStartedEvent Received"); } }CStopEventHandler
public class CStopEventHandler implements ApplicationListener<ContextStoppedEvent>{ public void onApplicationEvent(ContextStoppedEvent event) { System.out.println("ContextStoppedEvent Received"); } }MainApp.java
public class MainApp { public static void main(String[] args) { ConfigurableApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml"); // Let us raise a start event. context.start(); HelloWorld obj = (HelloWorld) context.getBean("helloWorld"); obj.getMessage(); // Let us raise a stop event. context.stop(); } }Beans
<?xml version = "1.0" encoding = "UTF-8"?> <beans xmlns = "http://www.springframework.org/schema/beans" xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation = "http://www.springframework.org/schema/beans "> <bean id = "helloWorld" class = "com.tutorialspoint.HelloWorld"> <property name = "message" value = "Hello World!"/> </bean> <bean id = "cStartEventHandler" class = "com.tutorialspoint.CStartEventHandler"/> <bean id = "cStopEventHandler" class = "com.tutorialspoint.CStopEventHandler"/> </beans>输出：
ContextStartedEvent Received Your Message : Hello World! ContextStoppedEvent Received 自定义Spring事件下边的案例将讲述如何编写和发布你自己的自定义事件
添加自定义事件CustomEvent.java,继承ApplicationEvent类
public class CustomEvent extends ApplicationEvent{ public CustomEvent(Object source) { super(source); } public String toString(){ return "My Custom Event"; } }添加自定义事件发布类CustomEventPublisher.java，实现ApplicationEventPublisherAware接口
public class CustomEventPublisher implements ApplicationEventPublisherAware { private ApplicationEventPublisher publisher; public void setApplicationEventPublisher (ApplicationEventPublisher publisher) { this.publisher = publisher; } public void publish() { CustomEvent ce = new CustomEvent(this); publisher.publishEvent(ce); } }自定义事件监听处理类，实现ApplicationListener
public class CustomEventHandler implements ApplicationListener<CustomEvent> { public void onApplicationEvent(CustomEvent event) { System.out.println(event.toString()); } }MainApp.java
public class MainApp { public static void main(String[] args) { ConfigurableApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml"); CustomEventPublisher cvp = (CustomEventPublisher) context.getBean("customEventPublisher"); cvp.publish(); cvp.publish(); } }Beans.xml
<beans xmlns = "http://www.springframework.org/schema/beans" xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation = "http://www.springframework.org/schema/beans "> <bean id = "customEventHandler" class = "com.tutorialspoint.CustomEventHandler"/> <bean id = "customEventPublisher" class = "com.tutorialspoint.CustomEventPublisher"/> </beans>