Data binding with immutable objects (Kotlin / Lombok / @ConstructorProperties) [SPR-15199]

[spring-projects-issues]

Benjamin M opened SPR-15199 and commented

I'm trying to integrate Lombok with my Spring Project. Now I came across the first issue:

@lombok.Value
public class MyGetParamContainer {
    String foo;
    int bar;
}

@RequestMapping(...)
public void foo(MyGetParamContainer params) {
    // ...
}

This will result in an Exception:

org.springframework.beans.BeanInstantiationException: Failed to instantiate [MyGetParamContainer]: No default constructor found

This happens because it's an immutable object, which sets all its values though its constructor.

Though it would be really nice if Spring could take care of @ConstructorProperties if there's no default constructor.

---

Affects: 4.3.6, 5.0 M4

Issue Links:

• Provide support for configuring the bindable properties of a form-backing object using field-level annotations [SPR-7747] #12403 Provide support for configuring the bindable properties of a form-backing object using field-level annotations
• Kotlin class instantiation with optional parameters and default values [SPR-15673] #20232 Kotlin class instantiation with optional parameters and default values
• Document functional configuration style [SPR-15049] #19615 Document functional configuration style
• Doc: First class support for java 8 parameter names API [SPR-13903] #18477 Doc: First class support for java 8 parameter names API
• 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
• Immutable object constructor arguments not considering WebDataBinder's FIELD_MARKER_PREFIX [SPR-15871] #20426 Immutable object constructor arguments not considering WebDataBinder's FIELD_MARKER_PREFIX

Referenced from: commits fa4d139, 65ba865

[spring-projects-issues]

Juergen Hoeller commented

This connects nicely to an ongoing theme of ours: allowing for a more functional style. Based on the JavaBeans ConstructorProperties mechanism (which we support for constructor argument resolution already) but also against Java 8 parameter name resolution, we'll consider a corresponding mode of data binding for 5.0 RC1.

On a related note, Jackson supports ConstructorProperties for JSON object binding as of 2.7:
FasterXML/jackson-databind#905

[spring-projects-issues]

Benjamin M commented

Yeah, I know that Jackson supports this.

I already can use Lombok with @RequestBody and @ResponseBody, which is awesome :)

[spring-projects-issues]

Aliaksei Zhynhiarouski commented

So, implementing this feature, it will also will add support of Kotlin data classes?

[spring-projects-issues]

Juergen Hoeller commented

Good point, this should easily work with Kotlin data classes as well...

[spring-projects-issues]

Juergen Hoeller commented

We're now automatically detecting data classes with a single public constructor, resolving the constructor arguments against the request parameters, as long as the parameter names are retained or an @ConstructorProperties annotation is declared. This works for Spring MVC as well as WebFlux.