Hibernate Validator: Method constraints not evaluated

I have a simple class, which I'd like to validate:

public class Model {
    @NotNull
    private String someField;

    @AssertTrue
    public boolean methodConstraint() { ... }
}

This class is validated as part of the inputs of a spring controller method.

I managed to configure the validation of the fields (someField in this case), but for some reason the methodConstraint() isn't even invoked, let alone validated. I remember this being possible.

I use the default Spring boot 2.6.6 configuration for validation, which means I use the 6.2.3 version of hibernate validator, with the 2.0.2 API version.

I suspect it is the ValidatorImpl:454 where thing go sideways, because this method only validates (direct) meta constraints, but method constraints don't seem to be considered as such.

Assuming you have something like

@Controller
class ModelController {
    ...
    public Result mappedMethod(@Valid Model model) {
        ...
    }
}

then the model will be validated as a JavaBean. Meaning only fields and getters will be considered.

If a model class is modified to:

public class Model {
    @NotNull
    private String someField;

    @AssertTrue
    public boolean isMethodConstraint() { ... }
}

where the constrained method starts following the JavaBean requirements (method name begins with is/get and has 0 parameters) then that method will be executed during the validation.

Alternatively, if beans do not follow the JavaBean format then a custom strategy can be used. See the documentation here. But if possible - it'll be easier just to update the model classes and make constrained methods start with is/get.