#RequestParam spring MVC , make one of two request params mandatory - web-services

Question

I am writing a service wherein I take in either an id or a location and I want to enforce the constraint that either the id or the location must be specified in my #Controller
#Controller
public class HelloController {
#RequestMapping(value="/loc.json",method = RequestMethod.GET)
public #ResponseBody String localiaztionRequest(#RequestParam(value = "location", required = false) String callback
,#RequestParam(value = "id", required = false) String uuid
,#RequestParam(value = "callback", required = false) String callback) {
//model.addAttribute("message", "Hello world!");
return "hello";
}
For clarity, I want each request to send either the location parameter or the id parameter. How do I enforce such a constraint on a pair of input parameters? Also as an aside could someone please explain to me the use of ModelMap , what is the effect of model.addAttribute("message","Hello World!") ?
Sorry if the questions seem rather naive, I'm extremely new to the spring framework.
Thanks in advance.

Answer 1

I think you should split it into two different controller methods
#RequestMapping(value="/loc.json",method = RequestMethod.GET, params={"location"})
public #ResponseBody String localizationRequestByLoc(#RequestParam String location, #RequestParam String callback) {
//model.addAttribute("message", "Hello world!");
return "hello";
}
#RequestMapping(value="/loc.json",method = RequestMethod.GET, params={"id"})
public #ResponseBody String localizationRequestById(#RequestParam String id, #RequestParam String callback) {
//model.addAttribute("message", "Hello world!");
return "hello";
}

Answer 2

One way to accomplish this (although indirect) would be to create a new object model representing the data to be passed in and another representing the data type and requiring both elements.
public enum MethodType
{
First,
Second
}
public class Filter
{
[Required]
public MethodType {get;set;}
[Required]
public string Data {get;set;}
}
use this object for the action method and view
and let the action method in the controller convert the object