Spring MVC: @EnableAsync needs to be redeclared for each ApplicationContext

[smfukaya]

I'm using spring-context-6.2.2.

Similar to SPR-16852, @EnableAsync must be redeclared for each ServletRegistrationBean because the AsyncAnnotationBeanPostProcessor registered in the root ApplicationContext is not inherited by the child ApplicationContext and there can only be one AsyncConfigurer.

@Configuration
@EnableWebMvc
public class MvcConfig implements WebMvcConfigurer {
    private static final String DISPATCHER_SERVLET_MAPPINGS_FORMAT = "/%s/*";
    @Bean
    ServletRegistrationBean<DispatcherServlet> api() {
        DispatcherServlet dispatcherServlet = new DispatcherServlet();
        AnnotationConfigWebApplicationContext applicationContext =
        		new AnnotationConfigWebApplicationContext();
        applicationContext.register(ApiConfig.class);
        dispatcherServlet.setApplicationContext(applicationContext);
        ServletRegistrationBean<DispatcherServlet> servletRegistrationBean =
        		new ServletRegistrationBean<>(
        				dispatcherServlet,
        				String.format(DISPATCHER_SERVLET_MAPPINGS_FORMAT, ApiConfig.API_SERVLET_NAME
        						)
        				);
        servletRegistrationBean.setName(ApiConfig.API_SERVLET_NAME);
        return servletRegistrationBean;
    }
}

@Configuration
@EnableAsync

@EnableWebMvc
@EnableAspectJAutoProxy(proxyTargetClass = true)
@EnableScheduling
@ComponentScan(basePackages = { "..." }
		, includeFilters = @Filter(Controller.class))
public class ApiConfig {
	public static final String API_SERVLET_NAME = "api";

	public ApiConfig() {

	}
}

I suggest adding a note to @EnableAsync Javadoc akin to what is provided by @EnableScheduling:

* <p><b>Note: {@code @EnableScheduling} applies to its local application context only,
* allowing for selective scheduling of beans at different levels. Please redeclare
* {@code @EnableScheduling} in each individual context, for example, the common root web
* application context and any separate {@code DispatcherServlet} application contexts,
* if you need to apply its behavior at multiple levels.