Support for @ModelAttribute dependency on webflux [SPR-16198]

Dongmin Shin opened SPR-16198 and commented

@ModelAttribute method arguments of @ModelAttribute annotated method are not resolved on webflux

@ModelAttribute("a")
public A attrA(@PathVariable String param1) {
    return new A(param1);
}

@ModelAttribute("b")
public B attrB(@ModelAttribute("a") A a, @RequestParam String param2) {
    // a.getParam1() is null
    return new B(a.getParam1(), param2);
}

cf.)

• spring webmvc
  https://github.com/spring-projects/spring-framework/blob/master/spring-web/src/main/java/org/springframework/web/method/annotation/ModelFactory.java#L131

• spring webflux
  https://github.com/spring-projects/spring-framework/blob/master/spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/ModelInitializer.java#L110

Affects: 5.0.1

References: pull request https://github.com/spring-projects/spring-framework/pull/2003

Compare the cited webflux ModelInitializer.java entry point with spring-web's ModelFactory.java behavior. Reproduce the @ModelAttribute example and trace how method arguments are resolved; done means the dependent @ModelAttribute receives the previously populated model attribute, with coverage for the demonstrated case.