Spring 事件原理及其应用

在 JDK 中已经提供相应的自定义事件发布功能的基础类:

• java.util.EventObject 类 ：自定义 事件 类型
• java.util.EventListener 接口：事件的 监听器

首先了解几个概念：

Spring 事件类结构

1. 事件类

事件类也就是定义发送的内容，比如可以通过继承 ApplicationContextEvent 来自定义一个特定事件类。

1.1 ApplicationEvent 类

首先是继承 EventObject 的 ApplicationEvent ，通过source来指定事件源：

public abstract class ApplicationEvent extends EventObject {
    /**
     * Constructs a prototypical Event.
     *
     * @param source The object on which the Event initially occurred.
     * @throws IllegalArgumentException if source is null.
     */
    public ApplicationEvent(Object source) {
        super(source);
    }
}

1.2 ApplicationContextEvent 类

是主要的容器事件，它有容器启动、刷新、停止以及关闭各种事件的子类。

public class ApplicationContextEvent extends ApplicationEvent {

    /**
     * Constructs a prototypical Event.
     *
     * @param source The object on which the Event initially occurred.
     * @throws IllegalArgumentException if source is null.
     */
    public ApplicationContextEvent(Object source) {
        super(source);
    }

    /**
     * Get the <code>ApplicationContext</code> that the event was raised for.
     */
    public final ApplicationContext getApplicationContext() {
        return (ApplicationContext) getSource();
    }

}

public class ContextClosedEvent extends ApplicationContextEvent{

    /**
     * Constructs a prototypical Event.
     *
     * @param source The object on which the Event initially occurred.
     * @throws IllegalArgumentException if source is null.
     */
    public ContextClosedEvent(Object source) {
        super(source);
    }

}

public class ContextRefreshedEvent extends ApplicationContextEvent{
    /**
     * Constructs a prototypical Event.
     *
     * @param source The object on which the Event initially occurred.
     * @throws IllegalArgumentException if source is null.
     */
    public ContextRefreshedEvent(Object source) {
        super(source);
    }

}

我们可以通过继承该类来实现，特定的事件类型需求，比如要实现一个邮件发送事件。只需要继承 ApplicationContextEvent 即可：

public class MailSe