CustomLocalValidatorFactoryBean.java

import org.hibernate.validator.HibernateValidator;
import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean;

import javax.validation.Configuration;
import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorFactory;

import java.util.List;

/**
 * A <code>LocalValidatorFactoryBean</code> that first tries to create a validator from a list of custom
 * <code>ConstraintValidator</code>s before the default behaviour.
 * <p>
 * Used in cases where the Custom Validator requires dependencies.
 * <p>
 * Usage:
 *
 * <pre>
 *     MyCustomValidator myCustomValidator = ...
 *     Validator validator = new CustomLocalValidatorFactoryBean(List.of(myCustomValidator)).getValidator();
 *
 *     validator.validate(myInstance);
 * </pre>
 */
public class CustomLocalValidatorFactoryBean extends LocalValidatorFactoryBean {

    private final List<ConstraintValidator<?, ?>> customConstraintValidators;

    public CustomLocalValidatorFactoryBean(List<ConstraintValidator<?, ?>> customConstraintValidators) {
        this.customConstraintValidators = customConstraintValidators;
        setProviderClass(HibernateValidator.class);
        afterPropertiesSet();
    }

    @Override
    protected void postProcessConfiguration(@NotNull Configuration<?> configuration) {
        super.postProcessConfiguration(configuration);

        ConstraintValidatorFactory defaultConstraintValidatorFactory =
            configuration.getDefaultConstraintValidatorFactory();

        configuration.constraintValidatorFactory(
            new ConstraintValidatorFactory() {
                @Override
                public <T extends ConstraintValidator<?, ?>> T getInstance(Class<T> key) {
                    for (ConstraintValidator<?, ?> constraintValidator : customConstraintValidators) {
                        if (key.equals(constraintValidator.getClass()))
                            return (T) constraintValidator;
                    }
                    return defaultConstraintValidatorFactory.getInstance(key);
                }

                @Override
                public void releaseInstance(ConstraintValidator<?, ?> instance) {
                    defaultConstraintValidatorFactory.releaseInstance(instance);
                }
            }
        );
    }

}