Spring validation for RequestBody parameters bound to collections in Controller methods

Question

I have

An Entity:

package org.ibp.soq;

public class MyEntity {

    private String field1;
    private String field2;

    //..get         


        

Answer 1

The solution is to create a custom Validator for Collection 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));
  }
}