How to bind @RequestParam to object in spring MVC?

Question

I want to make a POST request through AJAX, and I also want to bind the whole class object to the request, and I want to receive that request with @requestParam annotation. I know it can be done with @requestBody annotation, but I am curious to know: can we do it with @requestParam annotation?

An Ajax code:

var restDTO{
    id: 3,
    name: "hello"
}

 $.ajax({
          url: url, 
          type: 'POST',
          dataType: 'json',
          contentType: 'application/json',
          mimeType: 'application/json',
          data: JSON.stringify({RestDTO : restDTO}),          
          success: function(data) 
    {
    }

I do have RestDTO

Class RestDTO 
{

    int id;
    String name;

    //getter and setter

}

In controller

public String content(@RequestParam RestDTO restDTO){...}

What should I do the make this code run?

What should I change in sending data from ajax?

Do I need to change on server to receive an RestDto object with @requestParam annotation?

Answer 1

You can't, because @RequestParam just indicates, that one method's parameter should be bound to a one web request's parameter. It can't do mapping to objects. For use @RequestParam you should change ajax request:

var restDTO{
   id: 3,
   name: "hello"
}

 $.ajax({
          url: url, 
          type: 'POST',
          data: restDTO,          
          success: function(data){
             ....
          }
});

JQuery will send request as application/x-www-form-urlencoded and will process data to parameters automatically. You controller's method should look like following:

@RequestMapping("/url")
public String content(@RequestParam Long id, @RequestParam String name){...}

For automatically map parameters to object you can use @ModelAttribute annotation:

@RequestMapping("/url")
public String content(@ModelAttribute RestDTO restDTO){...}

In this case, names in javascript map should match to names of properties in RestDTO.

Generally, @ModelAttribute and @RequestBody created for same purposes: for binding data from request to method (whether objects of primitive type).

I consider, that @ModelAttribute is more convenient, when you working with html-forms and plain objects. There is ready to use Spring abilities like modelAttribute and path.

In its turn, @RequestBody more flexible, when you need manual control over data. Also, it is more convenient, when you're working with complex objects.

Personally me would prefer @RequestBody and json.

Answer 2

If you're sending your data as classic request params, you can bind to object by simply omitting the @RequestParam, so

public String content(RestDTO restDTO){...}

If you're sending json, you have to use @RequestBody.

If whysoever you're insisting on the @RequestParam, note that you can bind multiple values against a map, so

public String content(@RequestParam Map<String, String> restDTO){...}

From the @RequestParam doc

If the method parameter is Map or MultiValueMap and a parameter name is not specified, then the map parameter is populated with all request parameter names and values.