How do I send string as Springs’ @RequestParam using AngularJS?

In my backend (Spring controller) I have a method with @RequestParam String sentence as request param. I’d like to my a request (post) to this method by sending appropriate parameters.

In AngularJS I wrote:

$http.post('http://localhost:8080/wordCount', '?sentence=blah')

but backends return the error Required String parameter 'sentence' is not present"

Here’s my controller:

@RequestMapping(value = "wordCount", method = RequestMethod.POST)
public String count(@RequestParam(value = "sentence") String sentence) {

        //omitted
}

Source: AngularJS