如何通过代码注册一个Spring ApplicationListener实现？

我有一个 Spring 的实现ApplicationListener。当它在上下文 xml 文件中声明为 bean 或如果我使用时，它工作正常并接收事件@Component注解。

但是，如果我使用以下代码通过代码手动注册它，它不会接收事件ConfigurableListableBeanFactory's registerSingleton()方法。

我在下面添加了一些示例代码，描述了工作和不工作的情况。

自定义事件.java

package com.test.event;

import org.springframework.context.ApplicationEvent;

public class CustomEvent extends ApplicationEvent {

    public CustomEvent(Object source) {
        super(source);
    }

    public String toString() {
        return "My Custom Event";
    }
}

CustomEventPublisher.java

package com.test.event;

import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationEventPublisherAware;

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);
    }
}

自定义事件处理程序.java

package com.test.event;

import org.springframework.context.ApplicationListener;

public class CustomEventHandler 
   implements ApplicationListener<CustomEvent>{

   public void onApplicationEvent(CustomEvent event) {
      System.out.println(event.toString());
   }

}

applicationContextWithListenerBean.xml

<?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
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

   <bean id="customEventHandler" 
      class="com.test.event.CustomEventHandler"/>

   <bean id="customEventPublisher" 
      class="com.test.event.CustomEventPublisher"/>

</beans>

applicationContextWithoutListenerBean.xml

<?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
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

   <bean id="customEventPublisher" 
      class="com.test.event.CustomEventPublisher"/>

</beans>

主应用程序.java

package com.test.event;

import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
    public static void main(String[] args){

        /* The below code works fine when listener bean customEventHandler is defined in xml */

        ConfigurableApplicationContext context = new ClassPathXmlApplicationContext(
                "applicationContextWithListenerBean.xml");
        CustomEventPublisher cvp = (CustomEventPublisher) context
                .getBean("customEventPublisher");
        cvp.publish();
        context.close();

        /* The below code doesn't work when listener bean is registered through code. Is it possible to make this work? */

        ConfigurableApplicationContext context = new ClassPathXmlApplicationContext(
                "applicationContextWithoutListenerBean.xml");
        context.getBeanFactory().registerSingleton("customEventHandler",
                new CustomEventHandler());
        CustomEventPublisher cvp = (CustomEventPublisher) context
                .getBean("customEventPublisher");

        cvp.publish();
        context.close();
    }
}

是不是不能注册一个ApplicationListener通过代码？

将 bean 注册为单例将不会使其能够在 ApplicationEvents 上回调。

context.getBeanFactory().registerSingleton("customEventHandler",
            new CustomEventHandler());

应该改为

context.addApplicationListener(new CustomEventHandler());

这会将 ApplicationListener 实现添加到应用程序事件多播器 http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/context/event/ApplicationEventMulticaster.html它将事件发布到应用监听器 http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/context/ApplicationListener.html