spring 事件公布

spring 事件接口和注解

1.spring 事件中，能够公布原生的对象具体，也能够通过继承 ApplicationEvent 实现事件类。

1. ApplicationListener<E extends ApplicationEvent> 接口
   所有被 spring 托管的 bean 中，实现了该接口的类.
2. @EventListener(Clazz)
   间接公布原生对象，该对象不须要继承 ApplicationEvent 接口。在监听该事件时，间接应用注解标注本人承受的类型即可。

@Component
@Scope("prototype")
public class PersonEvent {@EventListener(Person.class)
    @Order(1)
    public void printPerson(Person person) throws Exception{System.out.println(person.toString());
    }
    @Setter
    @Getter
    @ToString
    public static class Person {
        private String name;
        private int age;
        private String address;
        public Person(String name, int age, String address) {
            this.name = name;
            this.age = age;
            this.address = address;
        }
    }
}
=======
private ApplicationContext applicationContext;
@Test
 public void test(){PersonEvent.Person person = new PersonEvent.Person("test", 3031, "wuhan");
    applicationContext.publishEvent(person);
}  

2. 异步事件和同步事件

spring 事件的公布流程，ApplicationContext 继承 ApplicationEventPublisher 接口，提供对外的公布接口。AbstractApplictionContext 外部提供了一个 applicationEventMulticaster。在容器 refresh 时，会执行 initApplicationEventMulticaster；

 protected void initApplicationEventMulticaster() {ConfigurableListableBeanFactory beanFactory = this.getBeanFactory();
        if (beanFactory.containsLocalBean("applicationEventMulticaster")) {this.applicationEventMulticaster = (ApplicationEventMulticaster)beanFactory.getBean("applicationEventMulticaster", ApplicationEventMulticaster.class);
            if (this.logger.isTraceEnabled()) {this.logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
            }
        } else {this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
            beanFactory.registerSingleton("applicationEventMulticaster", this.applicationEventMulticaster);
            if (this.logger.isTraceEnabled()) {this.logger.trace("No'applicationEventMulticaster'bean, using [" + this.applicationEventMulticaster.getClass().getSimpleName() + "]");
            }
        }
    }

spring 外部提供 SimpleApplicationEventMulticaster 外部的线程池没有初始化，所以 spring 的事件默认是同步事件。如果想要实现异步事件也很简略。间接向 spring 容器注册一个 SimpleApplicationEventMulticaster 即可。留神 bean 的名称为 applicationEventMulticaster

@Bean(name = "applicationEventMulticaster")
        public ApplicationEventMulticaster simpleApplicationEventMulticaster() {
            SimpleApplicationEventMulticaster eventMulticaster
                    = new SimpleApplicationEventMulticaster();
            SimpleAsyncTaskExecutor simpleAsyncTaskExecutor = new SimpleAsyncTaskExecutor();
            simpleAsyncTaskExecutor.setConcurrencyLimit(20);
            eventMulticaster.setTaskExecutor(simpleAsyncTaskExecutor);
            return eventMulticaster;
        }

SimpleApplicationEventMulticaster 事件散发器的散发流程

  public void multicastEvent(ApplicationEvent event, @Nullable ResolvableType eventType) {ResolvableType type = eventType != null ? eventType : this.resolveDefaultEventType(event);
        Executor executor = this.getTaskExecutor();
        Iterator var5 = this.getApplicationListeners(event, type).iterator();
        while(var5.hasNext()) {ApplicationListener<?> listener = (ApplicationListener)var5.next();
            if (executor != null) {executor.execute(() -> {this.invokeListener(listener, event);
                });
            } else {this.invokeListener(listener, event);
            }
        }
    }

从代码中看出，只有配置了异步线程池，所有的事件都会异步执行。

存在可能的集中需要问题

1. 同步事件时，事件监听有特定的执行程序怎么解决

   应用 spring 在解决监听 listener 时会进行 sort, AnnotationAwareOrderComparator.sort(allListeners); 所以能够通过 @Order 注解实现

2. 如果不想所有的事件都异步执行，有些异步，有些同步怎么解决

   本人笼罩 SimpleApplicationEventMulticaster 的 multicastEvent 散发办法，比方将异步事件类型退出全局的 map, 在其中的就走异步，否则走同步。