form:error message shows up in every field (List)

Question

I have some input fields that are members of an Arraylist of one object. I.E. The below code is inside a c:forEach loop.

<tr> <td><form:label path="person[${index}].firstname">First name</form:label></td> <td><form:input path="person[${index}].firstname" /></td> <td><form:errors path="person[${index}].firstname" cssClass="error" /></td> </tr>

This way the errors are not showing up at all. One the other hand, this code:

<tr> <td><form:label path="person[${index}].firstname">First name</form:label></td> <td><form:input path="person[${index}].firstname" /></td> <td><form:errors path="person.firstname" cssClass="error" /></td> </tr>

shows the errors but the errors are shown in every textfield of this page field.

Any ideas?

Answer 1

In your second approach,

<tr>
     <td><form:label path="person[${index}].firstname">First name</form:label></td>
     <td><form:input path="person[${index}].firstname" /></td>
     <td><form:errors path="person.firstname" cssClass="error" /></td>
</tr>

Spring will bind error message for attribute with every text box where you mapped <form:errors with path = person.firstname> It's correct spring behaviour.

There is no direct way to handle the error in way which you expect.

The solution is to create a custom Validator for Collection (List of object) and a @ControllerAdvice that registers that Validator in the WebDataBinders.

Validator :

import java.util.Collection;

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

/**
 * Spring {@link Validator} that iterates over the elements of a 
 * {@link Collection} and run the validation process for each of them
 * individually.
 *   
 * @author DISID CORPORATION S.L. (www.disid.com)
 */
public class CollectionValidator implements Validator {

  private final Validator validator;

  public CollectionValidator(LocalValidatorFactoryBean validatorFactory) {
    this.validator = validatorFactory;
  }

  @Override
  public boolean supports(Class<?> clazz) {
    return Collection.class.isAssignableFrom(clazz);
  }

  /**
   * Validate each element inside the supplied {@link Collection}.
   * 
   * The supplied errors instance is used to report the validation errors.
   * 
   * @param target the collection that is to be validated
   * @param errors contextual state about the validation process
   */
  @Override
  @SuppressWarnings("rawtypes")
  public void validate(Object target, Errors errors) {
    Collection collection = (Collection) target;
    for (Object object : collection) {
      ValidationUtils.invokeValidator(validator, object, errors);
    }
  }
}

ControllerAdvice :

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.InitBinder;

/**
 * Controller advice that adds the {@link CollectionValidator} to the 
 * {@link WebDataBinder}.
 * 
 * @author DISID CORPORATION S.L. (www.disid.com)
 */
@ControllerAdvice
public class ValidatorAdvice {

  @Autowired
  protected LocalValidatorFactoryBean validator;


  /**
   * Adds the {@link CollectionValidator} to the supplied 
   * {@link WebDataBinder}
   * 
   * @param binder web data binder.
   */
  @InitBinder
  public void initBinder(WebDataBinder binder) {
    binder.addValidators(new CollectionValidator(validator));
  }
}