Allow re-initialization of DataBinder to and from direct field or bean property access

[vghero]

Affects: Spring 5.0.9 / Boot 2.0.5

We have a Spring Web Mvc REST service implemented using complex nested DTO models which are validated using @Valid on controller method signatures. We created a global RestControllerAdvice which uses @InitBinder to set it to direct field access. This seems to work as expected.

Now we have one controller, that has to deal with bean property style models and needs a different InitBinder setup. Having the hope of being able to override the global default one, by specifying it on the special controller itself, sadly failed with an error message of the InitBinder about an already initialized binding. Also there does not seem to exist some kind of exclude parameter on RestControllerAdvice that would allow us to exclude that special controller.
Trying to use a special annotation on the other controllers and specifying it via annotations parameter on RestControllerAdvice also didn't work out during Mock Mvc Tests - ignoring the global one.

Finally, we ended up specifying @InitBinder on each controller separately - which works in all cases, but is quite cumbersome. Since we want to define the default globally and transparently for all controllers. Without having to remember, to specify packages, controller classes etc. on the global controller advice for new controllers to work properly - e.g. during validation.

Are there any plans to add some kind of exclude to the advice or being able to override a global default on controller level? This would be very helpful.

[rstoyanchev]

Global @InitBinder methods from @ControllerAdvice are invoked first, and @InitBinder methods from the target controller are invoked second. That means it should be possible to override the Validator locally via WebDataBinder#setValidator. I confirmed this works as expected, so please explain how to reproduce or provide a sample.

Note that I tried with Boot 2.2. Version 2.0 is no longer supported. In any case I think the behavior with regards to the order has been that way from the beginning.

[vghero]

Thanks for taking your time looking into this.

How does the validator relates to property-bean/direct-field access? If I take a look at this method, which we usually call to enable direct field access, I can't see any sign of validator setup. Is it somewhere hidden elsewhere?

	protected AbstractPropertyBindingResult createDirectFieldBindingResult() {
		DirectFieldBindingResult result = new DirectFieldBindingResult(getTarget(),
				getObjectName(), isAutoGrowNestedPaths());

		if (this.conversionService != null) {
			result.initConversion(this.conversionService);
		}
		if (this.messageCodesResolver != null) {
			result.setMessageCodesResolver(this.messageCodesResolver);
		}

		return result;
	}

It seems like DirectFieldBindingResult plays a role here? Isn't it like this is called after validation happens and constraint violations are processed?

[rstoyanchev]

I'm not sure to be honest because I don't know the details of how your global and the local method initialize the DataBinder. Please provide those.

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[vghero]

So based on the "complete" example:

git clone https://github.com/spring-guides/gs-serving-web-content.git

I adapted/added:

@ControllerAdvice
public class GlobalInitBinderControllerAdvice {

    @InitBinder
    public void enableDefaultDirectFieldAccess(DataBinder dataBinder) {
        dataBinder.initDirectFieldAccess();
    }
}

@Controller
public class GreetingController {

    @PostMapping("/greeting")
    public void greeting(@RequestBody @Valid GreetingDto greeting) {
	}
}

@Controller
public class Greeting2Controller {

    @InitBinder
    public void overrideGlobalAdviceToBeanPropertyAccess(DataBinder dataBinder) {
        dataBinder.initBeanPropertyAccess();
    }

    @PostMapping("/greeting2")
    public void greeting(@RequestBody @Valid GreetingDto greeting) {
    }
}

public class GreetingDto {

    @NotBlank
    public String greeting;
}

If I now post an empty JSON to /greeting then I get a 400 back. If I post the same to /greeting2 I get a 500 back, complaining about the already set DataBinder:

DataBinder is already initialized - call initBeanPropertyAccess before other configuration methods",

So my question was: is there a way to get a global default InitBinder setup applied and just override edge cases in the appropriate controllers? Or is there a way to exclude those edgecases in the global controller advice?