JavaBean Validation - Creating custom constraint Examples

package com.logicbig.example;

import javax.validation.*;
import javax.validation.executable.ExecutableValidator;
import java.lang.annotation.*;
import java.lang.reflect.Constructor;
import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.Set;

public class ConstructorReturnValidationExample {

    public static class Order {
        private final BigDecimal price;
        private final BigDecimal quantity;

        @ValidOrder
        public Order (BigDecimal price, BigDecimal quantity) {
            this.price = price;
            this.quantity = quantity;
        }

        public BigDecimal getPrice () {
            return price;
        }

        public BigDecimal getQuantity () {
            return quantity;
        }

        public BigDecimal getTotalPrice () {
            return (price != null && quantity != null ?
                    price.multiply(quantity) : BigDecimal.ZERO)
                    .setScale(2, RoundingMode.CEILING);
        }
    }

    public static void main (String[] args) throws NoSuchMethodException {
        Order order = new Order(new BigDecimal(4.5), new BigDecimal(10));
        Constructor<Order> constructor =
                            Order.class.getConstructor(BigDecimal.class, BigDecimal.class);

        Validator validator = getValidator();
        ExecutableValidator executableValidator = validator.forExecutables();
        Set<ConstraintViolation<Order>> constraintViolations =
                            executableValidator.validateConstructorReturnValue(constructor, order);

        if (constraintViolations.size() > 0) {
            constraintViolations.stream().forEach(
                                ConstructorReturnValidationExample::printError);
        } else {
            //proceed using order
            System.out.println(order);
        }
    }

    private static Validator getValidator(){
        Configuration<?> config = Validation.byDefaultProvider().configure();
        ValidatorFactory factory = config.buildValidatorFactory();
        Validator validator = factory.getValidator();
        factory.close();
        return validator;
    }

    private static void printError (
                        ConstraintViolation<Order> violation) {
        System.out.println(violation.getPropertyPath() + " " + violation.getMessage());
    }


    @Target({ElementType.CONSTRUCTOR, ElementType.ANNOTATION_TYPE})
    @Retention(RetentionPolicy.RUNTIME)
    @Constraint(validatedBy = OrderValidator.class)
    @Documented
    public static @interface ValidOrder {
        String message () default "total price must be 50 or greater for online order. " +
                            "Found: ${validatedValue.totalPrice}";

        Class<?>[] groups () default {};

        Class<? extends Payload>[] payload () default {};
    }


    public static class OrderValidator implements ConstraintValidator<ValidOrder, Order> {
        @Override
        public void initialize (ValidOrder constraintAnnotation) {
        }

        @Override
        public boolean isValid (Order order, ConstraintValidatorContext context) {
            if (order.getPrice() == null || order.getQuantity() == null) {
                return false;
            }
            return order.getTotalPrice()
                        .compareTo(new BigDecimal(50)) >= 0;

        }
    }
}

package com.logicbig.example;

import javax.validation.Constraint;
import javax.validation.Payload;
import java.lang.annotation.*;

@Target({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER,
        ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = LanguageValidator.class)
@Documented
public @interface Language {
    String message() default "must be a valid language display name." +
            " found: ${validatedValue}";

    Class<?>[] groups() default {};

    Class<? extends Payload>[] payload() default {};
}

package com.logicbig.example;

import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;
import java.util.Locale;

public class LanguageValidator implements ConstraintValidator<Language, String> {

    @Override
    public void initialize(Language constraintAnnotation) {
    }

    @Override
    public boolean isValid(String value, ConstraintValidatorContext context) {
        if (value == null) {
            return false;
        }
        for (Locale locale : Locale.getAvailableLocales()) {
            if (locale.getDisplayLanguage().equalsIgnoreCase(value)) {
                return true;
            }
        }

        return false;
    }
}

package com.logicbig.example;

class TestBean {
    @Language
    private String language;

    public String getLanguage() {
        return language;
    }

    public void setLanguage(String language) {
        this.language = language;
    }
}

package com.logicbig.example;

import javax.validation.*;

public class CustomConstraintExample {
    private static final Validator validator;

    static {
        Configuration<?> config = Validation.byDefaultProvider().configure();
        ValidatorFactory factory = config.buildValidatorFactory();
        validator = factory.getValidator();
        factory.close();
    }

    public static void main(String[] args) {
        TestBean testBean = new TestBean();
        testBean.setLanguage("englis");
        validator.validate(testBean).stream().forEach(CustomConstraintExample::printError);
    }

    private static void printError(ConstraintViolation<TestBean> violation) {
        System.out.println(violation.getPropertyPath() + " " + violation.getMessage());
    }

}