Immutable object constructor arguments not considering WebDataBinder's FIELD_MARKER_PREFIX [SPR-15871]

[spring-projects-issues]

Jean opened SPR-15871 and commented

Unchecked checkbox value should be recognized via WebDataBinder#fieldMarkerPrefix.

However when creating attribute, only constructor parameter names used, so field marker is not applied.

When this html form submit:

<form>
  <input type="checkbox" name="a" value="true">
  <input type="hidden" name="_a" value="on">
</form>

• kotlin code

@Controller
class TestController {
  class Form(val a: Boolean = true)
  
  @RequestMapping
  fun handle(@ModelAttribute form: Form) {
  }
}

when checkbox is unchecked, request should be:

?_a=on

and the value of form.a should be false, but currently it remains true.

---

spring-framework/spring-web/src/main/java/org/springframework/web/method/annotation/ModelAttributeMethodProcessor.java

Line 238 in 61cdc84

String[] paramNames = (cp != null ? cp.value() : parameterNameDiscoverer.getParameterNames(ctor));

---

Affects: 5.0 RC3

Issue Links:

• Data binding with immutable objects (Kotlin / Lombok / @ConstructorProperties) [SPR-15199] #19763 Data binding with immutable objects (Kotlin / Lombok / @ConstructorProperties)
• BindingResult support for constructor argument mismatch on immutable data object [SPR-15542] #20101 BindingResult support for constructor argument mismatch on immutable data object
• Revisit handling of missing fields (without default values) for immutable data classes [SPR-15877] #20432 Revisit handling of missing fields (without default values) for immutable data classes

Referenced from: commits 496223a, 9aa369f

[spring-projects-issues]

Juergen Hoeller commented

Good point! We're considering field default values as well as field markers for constructor arguments as well now, using the settings (and the getEmptyValue implementation) from the provided WebDataBinder.

[spring-projects-issues]

Jean commented

I love it. (y)
Also hope webflux catch up these changes about ModelAttribute binding.

[spring-projects-issues]

Juergen Hoeller commented

Indeed, I still need to port this and #19708 to WebFlux, possibly extracting some common delegate along the way. I'll wrap this up with #20432.