Document @Ordered interface use with SpringBootServletInitializer.

[apogrebnyak]

If a legacy web application need to register objects with Servlet framework before SpringBootServletInitializer.onStartup, it can implement it's own WebApplicationInitializer and provide the precedence through the Ordered interface.

SpringServletContainerInitializer sorts all discovered WebApplicationInitializers through AnnotationAwareOrderComparator class. In case if the WebApplicationInitializer does not implement Orderedinterface or is not annotated with @Order annotation, it is assigned LOWEST_PRECEDENCE.

I think it is better to add Ordered implementation to SpringBootServletInitializer and assign default precedence to 0.

This issue came as a work around after regression of #2070 failed

[philwebb]

Since SpringBootServletInitializer is abstract and always needs to be subclasses can you not just add @Ordered there?

[apogrebnyak]

Good point.

Should we add this advice to the class documentation?

BTW. For my original problem I've refactored the legacy initializer and plugged it directly into spring-boot framework.

I will say, that your framework significantly reduced boiler-plate Spring/Servlet components in my system. Thanks for a job well done.

-Alex

[philwebb]

I've added a hint to the Javadoc. Cheers.

[apogrebnyak]

Thank you,

-Alex