How does spring convert a Json string that is being passed to an object

Hi,
I am making the following post request : http://localhost:8080/api/users/create
with postman and body :
{ "userName" : "rohit", "email" : "rohit@xyz.com" }

In my controller i have :
@RequestMapping(value = "/api/users/create", method = RequestMethod.POST)
    @ResponseBody
    public APIPOSTResponse userAdd(@RequestBody User user)

And this perfectly converts json to the User object.
I read in docs that spring using a HttpMessageConverters for this.
When i navigated from intellij to MessageConverter interface i saw many classes implementing it.
They were all in spring-web jar.
I found one implementation which i suspected : MappingJackson2HttpMessageConverter will do the conversion and put break points in the decompiled source code the debugger didnt stop. Although it did stop
in the class AbstractHttpMessageConverter.
My understanding is based on the mediaType proper converter will be invoked. Want to confirm if this is correct with experts. Also what converter is executed for mediaType application/json ?

Thanks