Spring mvc controller jsr 303 basic list validation

Question

I have a simple MVC controller that takes a list of emails, and will then send a message to those emails.

json POST body

{"emailAddresses" : []} 

code

@RequestMapping(value = "/{id}/share", method = RequestMethod.POST)
@ResponseBody
public void shareThing(@PathVariable(value = "id") final String id, @Valid @NotEmpty       @RequestBody  final List<String> emailAddresses)

Basically, I want to use jsr-303 so that if the client posts a request with no emails, it fails. Preferably with a 401.

Should the above code work? Or what do I need to do? Here's the setup. Hibernate validator is on the classpath, so it should be picking up. However if I post an empty json array, it goes straight into the method with an empty array list as the bound parameter.

@Configuration
@EnableWebMvc
@ComponentScan(basePackages = {"com.package.thing"})
public class WeConfiguration extends WebMvcConfigurerAdapter

json POST body

{"emailAddresses" : []} 

code

@RequestMapping(value = "/{id}/share", method = RequestMethod.POST)
@ResponseBody
public void shareThing(@PathVariable(value = "id") final String id, @Valid @NotEmpty          @RequestBody  final List<String> emailAddresses, BindingResult bindingResult)
{
    System.out.println("Has Errors? " + bindingResult.hasErrors();
}

output

Has Errors? false

trial 3, changing payload, works... but I don't see the need to wrap?

public class EmailListDTO {

@NotEmpty
private List<String> emailAddresses;

public List<String> getEmailAddresses() {
    return emailAddresses;
}

public void setEmailAddresses(List<String> emailAddresses) {
    this.emailAddresses = emailAddresses;
}

}

 @RequestMapping(value = "/{id}/share", method = RequestMethod.POST)
@ResponseBody
public void shareThing(@PathVariable(value = "id") final String id, @Valid             @RequestBody  EmailListDTO emailListDTO, BindingResult bindingResult)
{
    System.out.println("Has Errors? " + bindingResult.hasErrors();
} 

json POST body

{"emailAddresses" : []} 

output

Has Errors? true

Answer 1

@Valid validates if the parameter class type itself has javax.validation annotations on fields. So it would use the Validator to scan the List class for validation annotations, which is not what you want.

You should wrap your List<String> into a DTO and change your parameter to that

public class MyListDTO {
    @NotEmpty 
    private List<String> emailAddresses;
    ... //getters and setters
}

@Valid doesn't just make it fail, it binds the error to a BindingResult object. If you add add a BindingResult parameter to your handler method (it must be next to your @Valid parameter)

 public void shareThing(@PathVariable(value = "id") final String id, @Valid @RequestBody final MyListDTO myDTO, BindingResult errors )

you can then checks the BindingResult for errors and choose what to do.