An Errors/BindingResult argument is expected to be declared immediately after the model attribute, the @RequestBody or the @RequestPart arguments

Question

I am teaching myself Spring by dissecting example applications and then adding code here and there to test theories that I develop during the dissection. I am getting the following error message when testing some code that I added to a Spring application:

An Errors/BindingResult argument is expected to be declared immediately after the  
model attribute, the @RequestBody or the @RequestPart arguments to which they apply  

The method to which the error message refers is:

@RequestMapping(value = "/catowners", method = RequestMethod.GET)
public String findOwnersOfPetType(Integer typeID, BindingResult result, Map<String, Object> model) {
    // find owners of a specific type of pet
    typeID = 1;//this is just a placeholder
    Collection<Owner> results = this.clinicService.findOwnerByPetType(typeID);
    model.put("selections", results);
    return "owners/catowners";
}  

This error message was triggered when I tried to load the /catowners url pattern in the web browser. I have reviewed this page and this posting, but the explanation does not seem clear.

Can anyone show me how to fix this error, and also explain what it means?

EDIT:
Based on Biju Kunjummen's response, I changed the syntax to the following:

@RequestMapping(value = "/catowners", method = RequestMethod.GET)
public String findOwnersOfPetType(@Valid Integer typeID, BindingResult result, Map<String, Object> model)  

I am still getting the same error message. Is ther something I am not understanding?

SECOND EDIT:

Based on Sotirios's comment, I changed the code to the following:

@RequestMapping(value = "/catowners", method = RequestMethod.GET)
public String findOwnersOfPetType(BindingResult result, Map<String, Object> model) {
    // find owners of a specific type of pet
    Integer typeID = 1;//this is just a placeholder
    Collection<Owner> results = this.clinicService.findOwnerByPetType(typeID);
    model.put("selections", results);
    return "owners/catowners";
 }

I am still getting the same error message after telling eclipse to run as...run on server again.

Is there something that I am not understanding?

Answer 1

Spring uses an interface called HandlerMethodArgumentResolver to resolve the parameter in your handler methods and construct an object to pass as an argument.

If it doesn't find one, it passes null (I have to verify this).

The BindingResult is a result object that holds errors that may have come up validating a @ModelAttribute, @Valid, @RequestBody or @RequestPart, so you can only use it with parameters that are annotated as such. There are HandlerMethodArgumentResolver for each of those annotations.

EDIT (response to comment)

Your example seems to show that the user should provide a pet type (as an integer). I would change the method to

@RequestMapping(value = "/catowners", method = RequestMethod.GET)
public String findOwnersOfPetType(@RequestParam("type") Integer typeID, Map<String, Object> model)

And you would make your request (depending on your config) as

localhost:8080/yourcontext/catowners?type=1

Here too there is nothing to validate so you don't want or need a BindingResult. It would fail if you tried to add it anyway.

Answer 2

If you have a parameter of type BindingResult it is essentially to hold any errors when binding http request parameters to a variable declared directly preceding the BindingResult method parameter.

So all of these is acceptable:

@RequestMapping(value = "/catowners", method = RequestMethod.GET)
public String findOwnersOfPetType(@Valid MyType type, BindingResult result, ...)


@RequestMapping(value = "/catowners", method = RequestMethod.GET)
public String findOwnersOfPetType(@ModelAttribute MyType type, BindingResult result, ...)

@RequestMapping(value = "/catowners", method = RequestMethod.GET)
public String findOwnersOfPetType(@RequestBody @Valid MyType type, BindingResult result, ...)