spring-boot - 无法在 Spring Boot 中拦截 ApplicationEnvironmentPreparedEvent

Question

我需要以编程方式设置一些系统属性，我认为最好的方法是在事件监听器中进行一次 ApplicationEnvironmentPreparedEvent被拦截了。
但问题是我无法在我的听众中捕捉到那个事件。

@Component
public class AppListener {

    @EventListener
    public void onApplicationEvent(ApplicationEvent event) {
        if (event instanceof ApplicationEnvironmentPreparedEvent) {
            System.setProperty("java.util.concurrent.ForkJoinPool.common.threadFactory", MyThreadFactory.class.getName());
        }
    }

}

我做错了什么，为什么我不能 catch 那个事件？

Answer 1

来自 Spring Boot documentation :

Some events are actually triggered before the ApplicationContext is created, so you cannot register a listener on those as a @Bean. You can register them with the SpringApplication.addListeners(…​) method or the SpringApplicationBuilder.listeners(…​) method.

来自 Spring documentation (这适用于 5.1.7 版):

Processing of @EventListener annotations is performed via the internal EventListenerMethodProcessor bean which gets registered automatically when using Java config or manually via the or element when using XML config.

所以ApplicationEnvironmentPreparedEvent(以及所有的Spring Boot应用事件)发生在context和bean创建之前，而@EventListener是由bean控制的，所以此时@EventListener注解无法被拾取。您必须专门创建一个监听器类并显式添加它以捕获此事件(或在创建 bean 之前发生的任何事件)。

你的类:

public class AppListener implements ApplicationListener<ApplicationEnvironmentPreparedEvent>
{
    @Override
    public void onApplicationEvent(ApplicationEnvironmentPreparedEvent event)
    {
        System.setProperty("java.util.concurrent.ForkJoinPool.common.threadFactory",
                MyThreadFactory.class.getName());
    }
}

...以及相关的 SpringApplicationBuilder 代码:

ConfigurableApplicationContext context = new SpringApplicationBuilder(Launcher.class)
            .listeners(new AppListener()).run();