Controller does not accept data POST 404

Help me please, I'm writing a site on java ee with spring mvc, I need to send the request to the servlet, but I get error 404.

my html:

<input type="button" value="add" onclick="sendRequest()">

my js:

function sendRequest(){
var str = "this is string";
    $.ajax({
            url:"ajaxtest",
            type:"POST",
            //data:JSON.stringify(myJson).toString(),
            data:str,
            success: alert("good")
        });}

my controller:

@RequestMapping(value="ajaxtest", method=RequestMethod.POST)
    public void getAjax(String myStr){
        System.out.print("result : "+myStr);
    }

result console browser:

POST http://localhost/MyProject/ajaxtest 404 (Not Found)
m.ajaxTransport.send - jquery-1.11.2.min.js:4 
m.extend.ajax - jquery-1.11.2.min.js:4
sendRequest - add.jsp:139
onclick - add.jsp:213

result console ide:

INFO: Server startup in 2991 ms
result : null

Please help me!