Spring validation for RequestBody parameters bound to collections in Controller methods - spring

Question

I have
An Entity:
package org.ibp.soq;
public class MyEntity {
private String field1;
private String field2;
//..getters and setters
}
Validator for the entity:
package org.ibp.soq;
import org.springframework.stereotype.Component;
import org.springframework.validation.Errors;
import org.springframework.validation.Validator;
#Component
public class MyEntityValidator implements Validator {
#Override
public boolean supports(Class<?> clazz) {
return MyEntity.class.equals(clazz);
}
#Override
public void validate(Object target, Errors errors) {
MyEntity myEntity = (MyEntity) target;
// Logic to validate my entity
System.out.print(myEntity);
}
}
and
The REST controller with bulk PUT method:
package org.ibp.soq;
import java.util.List;
import javax.validation.Valid;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.annotation.InitBinder;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;
#RestController
#RequestMapping("/myEntity")
public class MyEntityRestResource {
#Autowired
private MyEntityValidator myEntityValidator;
#InitBinder
protected void initBinder(final WebDataBinder binder) {
binder.addValidators(this.myEntityValidator);
}
#RequestMapping(method = RequestMethod.PUT)
public void bulkCreate(#RequestBody #Valid List<MyEntity> myEntities) {
// Logic to bulk create entities here.
System.out.print(myEntities);
}
}
When I make a PUT request to this resource with following request body:
[
{
"field1": "AA",
"field2": "11"
},
{
"field1": "BB",
"field2": "22"
}
]
The error I get is:
"Invalid target for Validator [org.ibp.soq.MyEntityValidator#4eab617e]: [org.ibp.soq.MyEntity#21cebf1c, org.ibp.soq.MyEntity#c64d89b]"
I can understand that this is because MyEntityValidator "supports" single MyEntity validation, not validation for ArrayList<MyEntity>.
MyEntityValidator works perfectly if I have single MyEntity object in request body and a corresponding controller method with #RequestBody #Valid MyEntity myEntity parameter.
How can the validator setup I have used, be extended for supporting validation of collection of MyEntity's ?

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));
}
}

Answer 2

As you might have guessed this cannot be achieved using Spring Validation. Spring Validation implements Bean Validation(JSR 303/349) as opposed to Object validation. Unfortunately a collection is not a Java Bean. You have two options
Wrap your list inside a Java Bean
Call the validator manually in your bulk create method myEntityValidator. validate(targetObject, errors).

Answer 3

Actually, this can be achieved using Spring Validation and JSR303.
Expose a MethodValidationPostProcessor bean.
Annotate your controller class with #Validated (org.springframework.validation.annotation.Validated)
Use the JSR303 validation annotations on your MyEntity fields/methods.
Annotate your RequestBody argument with #Valid (you've already done this in your example).
Add an #ExceptionHandler method to handle MethodArgumentNotValidException. This can be done in the controller or in a #ControllerAdvice class.