ItemValidator.java

package eMarket.controller;

import org.springframework.validation.Errors;
import org.springframework.validation.ValidationUtils;
import org.springframework.validation.Validator;

public class ItemValidator implements Validator {

    public boolean supports(Class<?> clazz) {
        return ItemFormDto.class.equals(clazz);
    }

    @Override
	public void validate(Object target, Errors errors) {
		ItemFormDto dto = (ItemFormDto) target;

		ValidationUtils.rejectIfEmptyOrWhitespace(errors, "productId", "", "Field cannot be empty.");
		ValidationUtils.rejectIfEmptyOrWhitespace(errors, "amount", "", "Field cannot be empty.");
		
		if (dto.getAmount() <= 0) {
			errors.rejectValue("amount", "", "Please Enter a Positive Amount");
		}
		// no item selected
		if(dto.getProductId() < 0) {
			errors.rejectValue("productId","","Please Select A product");
		}
		
	}

}