经过一点实验，我发现ContextClosedEvent上的ApplicationListener总是在调用任何@PreDestroy方法或任何bean的destroyMethod之前执行，也就是说，总是先调用onApplicationEvent(ContextClosedEvent event)。
一个例子是：

@Component
public class PriorityShutdownListener implements ApplicationListener<ContextClosedEvent> {
    
    @Autowired
    private Server grpcServer;
    
    /**
     * This blocking code will be executed before any 
     * @PreDestroy method or bean's `destroyMethod` is called.
     */
    @Override
    public void onApplicationEvent(ContextClosedEvent event) {
        grpcServer.shutdown();
        // don't forget to await for existing
        // calls to finish before returning from this method
    }
}