当前位置：首页 > news >正文

ApplicationContext 事件发布与监听机制详解

news 2025/7/19 7:23:06

ApplicationContext 事件发布与监听机制详解

ApplicationContext 接口是 Spring 框架的核心容器接口，它提供了事件发布与监听机制，允许应用程序组件之间通过事件进行松耦合通信。这种机制基于观察者模式，实现了发布-订阅模型。

核心概念

事件(ApplicationEvent): 所有事件类的基类，Spring 提供了多种内置事件
事件发布者(ApplicationEventPublisher): 发布事件的接口，ApplicationContext 实现了此接口
事件监听器(ApplicationListener): 监听特定事件的接口

主要方法

1. 事件发布相关方法

publishEvent(Object event): 发布事件（在 Spring 4.2+ 中，可以直接发布任何对象作为事件）
publishEvent(ApplicationEvent event): 发布标准 ApplicationEvent 事件

2. 事件监听相关方法

通过实现 ApplicationListener<E extends ApplicationEvent> 接口
或使用 @EventListener 注解（Spring 4.2+ 推荐方式）

内置事件类型

Spring 提供了一些内置事件：

ContextRefreshedEvent: ApplicationContext 初始化或刷新时触发
ContextStartedEvent: ApplicationContext 启动时触发
ContextStoppedEvent: ApplicationContext 停止时触发
ContextClosedEvent: ApplicationContext 关闭时触发
RequestHandledEvent: Web 请求处理完成时触发（仅适用于 Web 应用）

实现方式

方式1：实现 ApplicationListener 接口

import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.stereotype.Component;@Component
public class MyContextRefreshedListener implements ApplicationListener<ContextRefreshedEvent> {@Overridepublic void onApplicationEvent(ContextRefreshedEvent event) {System.out.println("Context refreshed event received!");}
}

方式2：使用 @EventListener 注解（推荐）

import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;@Component
public class MyEventListener {@EventListenerpublic void handleContextRefresh(ContextRefreshedEvent event) {System.out.println("Context refreshed event handled via @EventListener!");}// 可以监听多个事件类型@EventListener({ContextStartedEvent.class, ContextStoppedEvent.class})public void handleMultipleEvents(ApplicationEvent event) {if (event instanceof ContextStartedEvent) {System.out.println("Context started event received");} else if (event instanceof ContextStoppedEvent) {System.out.println("Context stopped event received");}}
}

方式3：自定义事件

定义自定义事件类：

import org.springframework.context.ApplicationEvent;public class CustomEvent extends ApplicationEvent {private String message;public CustomEvent(Object source, String message) {super(source);this.message = message;}public String getMessage() {return message;}
}

创建事件发布者：

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.stereotype.Service;@Service
public class EventPublisherService {@Autowiredprivate ApplicationEventPublisher eventPublisher;public void publishCustomEvent(String message) {System.out.println("Publishing custom event...");CustomEvent event = new CustomEvent(this, message);eventPublisher.publishEvent(event);}
}

创建事件监听器：

import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;@Component
public class CustomEventListener {@EventListenerpublic void handleCustomEvent(CustomEvent event) {System.out.println("Received custom event - Message: " + event.getMessage());}
}

完整示例

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationListener;
import org.springframework.context.annotation.Bean;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;@SpringBootApplication
public class EventApplication {public static void main(String[] args) {SpringApplication.run(EventApplication.class, args);}
}// 自定义事件
class OrderCreatedEvent {private final String orderId;public OrderCreatedEvent(String orderId) {this.orderId = orderId;}public String getOrderId() {return orderId;}
}// 事件发布服务
@Component
class OrderService {private final ApplicationEventPublisher eventPublisher;public OrderService(ApplicationEventPublisher eventPublisher) {this.eventPublisher = eventPublisher;}public void createOrder(String orderId) {System.out.println("Creating order: " + orderId);// 业务逻辑...eventPublisher.publishEvent(new OrderCreatedEvent(orderId));}
}// 方式1：实现 ApplicationListener 接口
@Component
class OrderNotificationListener implements ApplicationListener<OrderCreatedEvent> {@Overridepublic void onApplicationEvent(OrderCreatedEvent event) {System.out.println("Sending notification for order: " + event.getOrderId());}
}// 方式2：使用 @EventListener 注解
@Component
class OrderInventoryListener {@EventListenerpublic void updateInventory(OrderCreatedEvent event) {System.out.println("Updating inventory for order: " + event.getOrderId());}
}// 监听内置事件
@Component
class ContextStartupListener {@EventListenerpublic void onContextRefreshed(ContextRefreshedEvent event) {System.out.println("Application context has been refreshed!");}
}

异步事件处理

要使事件监听异步执行，可以添加 @Async 注解：

首先在配置类上启用异步支持：

import org.springframework.context.annotation.Configuration;
import org.springframework.scheduling.annotation.EnableAsync;@Configuration
@EnableAsync
public class AsyncConfig {
}

然后在监听方法上添加 @Async：

import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Component;@Component
public class AsyncEventListener {@Async@EventListenerpublic void handleAsyncEvent(OrderCreatedEvent event) {System.out.println("Processing event asynchronously for order: " + event.getOrderId());try {Thread.sleep(2000); // 模拟耗时操作} catch (InterruptedException e) {Thread.currentThread().interrupt();}System.out.println("Async processing completed for order: " + event.getOrderId());}
}

事件传播顺序

如果需要控制多个监听器的执行顺序，可以使用 @Order 注解：

import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;@Component
@Order(1)
class FirstOrderListener {@EventListenerpublic void handleFirst(OrderCreatedEvent event) {System.out.println("First listener for order: " + event.getOrderId());}
}@Component
@Order(2)
class SecondOrderListener {@EventListenerpublic void handleSecond(OrderCreatedEvent event) {System.out.println("Second listener for order: " + event.getOrderId());}
}