Build own new message from BindingResult - spring

Question

I would like to consult you about the BindingResult. Take a look at my situation below.
My messages.properties store error message as follows
error.required=Please input {0}
My controller has rejected 2 fields with the same error as follows
bidingResult.rejectValue("field1", "error.required", new Object[]{"Field1"}, null);
bidingResult.rejectValue("field2", "error.required", new Object[]{"Filed2"}, null);
My view has extract messages by used Thymeleaf syntax as follows
<div th:each="err : ${#fields.errors('*')}" th:text="${err}"></div>
The result will show 2 messages as follows
Please input Field1
Please input Field2
My question is can I create a new messages object by BindingResult to show a message like this
Please input Field1 and Field2
I want to merge the same error together and concatenate message param

Answer 1

The easiest way to do that will be to create a custom validator at the object level. Start with a custom annotation:
import javax.validation.Constraint;
import javax.validation.Payload;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
#Target(ElementType.TYPE)
#Retention(RetentionPolicy.RUNTIME)
#Constraint(validatedBy = BothFieldsPresentValidator.class)
public #interface BothFieldsPresent {
String message() default "{BothFieldsPresent}";
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
}
Next, create the custom validator:
public class BothFieldsPresentValidator implements ConstraintValidator<BothFieldsPresent, MyObject> {
public boolean isValid(MyObject myObject, ConstraintValidatorContext context) {
if( myObject.getField1() == null && myObject.getField2() == null ) {
context.disableDefaultConstraintViolation();
context.buildConstraintViolationWithTemplate("{BothFieldsPresent}")
.addConstraintViolation()
return false;
}
return true;
}
}
Add the new custom annotation to your MyObject class:
#BothFieldsPresent
public class MyObject {
...
}
In your controller, do something like this:
#PostMapping
public String doPost(#Valid #ModelAttribute("myObject") MyObject myObject, BindingResult bindingResult, Model model) {
if( bindingResult.hasErrors() ) {
return "template-name"
}
service.doSomething(myObject);
return "redirect:/somewhere"
}
Add this to messages.properties:
BothFieldsPresent=Please input Field1 and Field2