Startup time optimization - eliminate expensive bean creations

[cslee00]

Continued analysis of startup time (Spring container, not Boot) shows several unnecessary (default) beans created. These can be avoided by providing a minimal set (instead of relying on defaults).

Unclear if these could/should be rolled into the container (that would be nice as an optional flag) or a documentation issue.

@Configuration
@ComponentScan("mypackage.controller")
public class AppConfig {

    /*
     * Create required HandlerMapping, to avoid several default HandlerMapping instances being created
     */
    @Bean
    public HandlerMapping handlerMapping() {
        return new RequestMappingHandlerMapping();
    }

    /*
     * Create required HandlerAdapter, to avoid several default HandlerAdapter instances being created
     */
    @Bean
    public HandlerAdapter handlerAdapter() {
        return new RequestMappingHandlerAdapter();
    }

    /*
     * optimization - avoids creating default exception resolvers; not required as the serverless container handles
     * all exceptions
     *
     * By default, an ExceptionHandlerExceptionResolver is created which creates many dependent object, including
     * an expensive ObjectMapper instance.
     */
    @Bean
    public HandlerExceptionResolver handlerExceptionResolver() {
        return new HandlerExceptionResolver() {
            @Nullable
            @Override
            public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex) {
                return null;
            }
        };
    }
}```

[cslee00]

In addition to reducing startup time, the above config improves security by removing unnecessary components such as BeanNameUrlHandlerMapping.

[sapessi]

This are great tips. I'll make sure to include them in the documentation. I'll close this issue for now and refer to the original issue #33.