Consider adding PlusConfiguration and AnnotationConfiguration to jetty WebAppContext

[nyilmaz]

Since jetty-annotations and jetty-plus dependencies are available via websocket, AnnotationConfiguration and PlusConfiguration can be added in JettyEmbeddedServletContainerFactory. This will enable, for example, annotations like @MultipartConfig are picked up and registered by jetty.

[wilkinsona]

Unfortunately, I don't think we should do this. As described in the documentation:

Embedded servlet containers will not directly execute the Servlet 3.0+ javax.servlet.ServletContainerInitializer interface, or Spring’s org.springframework.web.WebApplicationInitializer interface.

This is an intentional design decision intended to reduce the risk that 3rd party libraries designed to run inside a war will break Spring Boot applications.

You can use Boot's own @ServletComponentScan to have it scan for and automatically register @WebServlet, @WebFilter and @WebListener beans with the container. Now that #6680 has been fixed, it'll also honour @MultipartConfig.