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spring ApplicationContext的事件监听机制

article 2025/1/23 9:37:24

测试代码

继承ApplicationEvent定义自己的事件

public class MyEvent extends ApplicationEvent {
    String message;

    public MyEvent(Object source, String message) {
        super(source);
        this.message = message;
    }

    public String getMessage() {
        return message;
    }

}

实现ApplicationListener接口定义listener

eg:

@Component
public class MyEventListener implements ApplicationListener<MyEvent> {
    @Override
    public void onApplicationEvent(MyEvent event) {
        System.out.println("MyEventListener received: " + event.getMessage());
    }
}

事件发布

@Service
public class MyEventPublisher {

    @Autowired
    private ApplicationContext context;

    public void publish(String message) {
        MyEvent myEvent = new MyEvent(this, message);
        context.publishEvent(myEvent);
    }
}

测试controller中测试发布事件

@RestController
public class TestControl {

    @Autowired
    private MyEventPublisher myEventPublisher;


    @GetMapping(value = "/test")
    public String getTest(@Param("msg") String msg) {
        myEventPublisher.publish(msg);
        return "hello test";
    }

测试输出：

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原理

事件如何发布

本例用springboot开启一个web项目，内置了ApplicationContext bean 直接获取到，然后就可以发布事件了
在这里插入图片描述

org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext

走到
org.springframework.context.support.AbstractApplicationContext#publishEvent(org.springframework.context.ApplicationEvent)，广播事件

在这里插入图片描述

获取到对应事件类型监听器，然后丢到线程池去执行

@Override
public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
	ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
	for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) {
		Executor executor = getTaskExecutor();
		if (executor != null) {
			executor.execute(() -> invokeListener(listener, event));
		}
		else {
			invokeListener(listener, event);
		}
	}
}

调用listener的onApplicationEvent方法

private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) {
	try {
		listener.onApplicationEvent(event);
	}
	catch (ClassCastException ex) {
		String msg = ex.getMessage();
		if (msg == null || matchesClassCastMessage(msg, event.getClass())) {
			// Possibly a lambda-defined listener which we could not resolve the generic event type for
			// -> let's suppress the exception and just log a debug message.
			Log logger = LogFactory.getLog(getClass());
			if (logger.isDebugEnabled()) {
				logger.debug("Non-matching event type for listener: " + listener, ex);
			}
		}
		else {
			throw ex;
		}
	}
}