Spring MVC how @RequestBody works

I thought that @RequestBody tries to map request params to the object after the annotation by the property names.

But if I got:

@RequestMapping(value = "/form", method = RequestMethod.GET)
public @ResponseBody Person formGet(@RequestBody Person p,ModelMap model) {
    return p;
}

The request:

http://localhost:8080/proj/home/form?id=2&name=asd

Return 415

When I change @RequestBody Person p with @RequestParam Map<String, String> params it's OK:

@RequestMapping(value = "/form", method = RequestMethod.GET)
public @ResponseBody Person formGet(@RequestParam Map<String, String> params) {
        return new Person();
}

Person class:

public class Person{
    private long id;
    private String name;

    public Person() {
    }

    public Person(long id, String name) {
        super();
        this.id = id;
        this.name = name;
    }
    public long getId() {
        return id;
    }
    public void setId(long id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

Spring vresion 3.2.3.RELEASE

Where did I go wrong?