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事件机制是Spring的一个功能，目前我们使用了SpringBoot框架，所以记录下事件机制在SpringBoot框架下的使用，同时实现异步处理。事件机制其实就是使用了观察者模式(发布-订阅模式)。

Spring的事件机制经过如下流程：

• 1、自定义事件，继承org.springframework.context.ApplicationEvent抽象类
• 2、定义事件监听器，实现org.springframework.context.ApplicationListener接口
• 3、在Spring容器中发布事件

SpringBoot的实例程序

实现一个保存用户的时候，向用户提供的邮箱发送一封邮件的功能，同时采用异步处理。

自定义事件

import org.springframework.context.ApplicationEvent;public class EmailEvent extends ApplicationEvent {private static final long serialVersionUID = 3733891603598996786L;private String emailAddress;public EmailEvent(String emailAddress) {super(emailAddress);this.emailAddress = emailAddress;}public String getEmailAddress() {return emailAddress;}public void setEmailAddress(String emailAddress) {this.emailAddress = emailAddress;}
}

定义事件监听器

import java.util.concurrent.TimeUnit;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.ApplicationListener;
import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Component;@Component
public class EmailEventListener implements ApplicationListener<EmailEvent> {private static Logger log = LoggerFactory.getLogger(EmailEventListener.class);// 异步处理@Async@Overridepublic void onApplicationEvent(EmailEvent event) {log.info("监听到事件--邮箱地址:" + event.getEmailAddress());//模拟处理的耗时3stry {TimeUnit.SECONDS.sleep(3);} catch (InterruptedException e) {e.printStackTrace();}log.info("事件处理完成");}}

发布事件

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.stereotype.Component;@Component
public class EmailEventPublish {@Autowiredprivate ApplicationContext applicationContext;public void publishEvent(String emailAddress) {EmailEvent event = new EmailEvent(emailAddress);applicationContext.publishEvent(event);}}

调用事件

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;import com.example.demo.event.EmailEventPublish;@RestController
public class EventController {private static Logger log = LoggerFactory.getLogger(EventController.class);@Autowiredprivate EmailEventPublish emailEventPublish;@RequestMapping("/event")public void publishEvent(@RequestParam String emailAddress) {// 发布事件 -- 采用异步处理emailEventPublish.publishEvent(emailAddress);// 正常该语句先执行log.info("Controller业务处理");}
}

结果

访问如下地址

http://localhost:8080/event?emailAddress=[e-mail]

结果为

2023-08-04 21:21:14.338  INFO 6400 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring FrameworkServlet 'dispatcherServlet'
2023-08-04 21:21:14.338  INFO 6400 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : FrameworkServlet 'dispatcherServlet': initialization started
2023-08-04 21:21:14.370  INFO 6400 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : FrameworkServlet 'dispatcherServlet': initialization completed in 32 ms
2023-08-04 21:21:14.429  INFO 6400 --- [nio-8080-exec-1] .s.a.AnnotationAsyncExecutionInterceptor : No task executor bean found for async processing: no bean of type TaskExecutor and no bean named 'taskExecutor' either
2023-08-04 21:21:14.534  INFO 6400 --- [nio-8080-exec-1] c.e.demo.controller.EventController      : Controller业务处理
2023-08-04 21:21:14.535  INFO 6400 --- [cTaskExecutor-1] c.example.demo.event.EmailEventListener  : 监听到事件--邮箱地址:[e-mail]
2023-08-04 21:21:17.536  INFO 6400 --- [cTaskExecutor-1] c.example.demo.event.EmailEventListener  : 事件处理完成

上述结果可知是实现了异步处理，先打印了事件之后的程序，等时间到再执行监听程序的代码。

实现异步处理就是在监听事件执行业务代码的方法上添加@Async注解，同时在启动类上添加@EnableAsync即可。

上面的日志还提到了TaskExecutor,这是如果有自定义的线程池就会去调用，如果没有就用默认的。我们也可以自己定义一个TaskExecutor。

import org.springframework.aop.interceptor.AsyncUncaughtExceptionHandler;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.lang.Nullable;
import org.springframework.scheduling.annotation.AsyncConfigurer;
import org.springframework.scheduling.annotation.EnableAsync;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;import java.util.concurrent.Executor;
import java.util.concurrent.ThreadPoolExecutor;@EnableAsync
@Configuration
public class ThreadPool implements AsyncConfigurer {@Nullable@Override@Bean("taskExecutor")public Executor getAsyncExecutor() {ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();// 线程池创建时候初始化的线程数executor.setCorePoolSize(10);// 线程池最大的线程数，只有在缓冲队列满了之后才会申请超过核心线程数的线程executor.setMaxPoolSize(20);// 用来缓冲执行任务的队列executor.setQueueCapacity(200);// 允许线程的空闲时间60秒executor.setKeepAliveSeconds(60);// 线程池名的前缀executor.setThreadNamePrefix("taskExecutor-");// 线程池对拒绝任务的处理策略executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());executor.initialize();return executor;}@Nullable@Overridepublic AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {return null;}
}

结果

2023-08-04 21:27:36.507  INFO 7848 --- [nio-8080-exec-2] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring FrameworkServlet 'dispatcherServlet'
2023-08-04 21:27:36.507  INFO 7848 --- [nio-8080-exec-2] o.s.web.servlet.DispatcherServlet        : FrameworkServlet 'dispatcherServlet': initialization started
2023-08-04 21:27:36.537  INFO 7848 --- [nio-8080-exec-2] o.s.web.servlet.DispatcherServlet        : FrameworkServlet 'dispatcherServlet': initialization completed in 30 ms
2023-08-04 21:27:36.757  INFO 7848 --- [nio-8080-exec-2] c.e.demo.controller.EventController      : Controller业务处理
2023-08-04 21:27:36.757  INFO 7848 --- [ taskExecutor-1] c.example.demo.event.EmailEventListener  : 监听到事件--邮箱地址:[e-mail]
2023-08-04 21:27:39.757  INFO 7848 --- [ taskExecutor-1] c.example.demo.event.EmailEventListener  : 事件处理完成

可知是使用我们定义的线程池[ taskExecutor-1] 。

总结

Spring的事件机制是一个很实用的一个功能，在监听和异步处理相关的功能比较适合。