Reach Java Servlet from JavaScript

Question

How can reach a JavaServlet from JavaScript?

My html-File in the path P08_BillBoard/web/billboard.html . Addtionally, the billboard.js is in the same directory. The servlet-File is in P08_BillBoard/src/java/de/vs/Billboard.java .

Now, if I try to run the application, I get the following error from the browser:

POSThttp://localhost:63342/P08_BillBoard/web/BillBoardServer

404 Not Found

The code of the POST-Request in the billboard.js is:

function postHttpRequest(url) {
    var xmlhttp = getXMLHttpRequest(); 
    xmlhttp.open("POST", url, true);
    xmlhttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
    xmlhttp.onreadystatechange = function() {
        if(xmlhttp.readyState == 4 && xmlhttp.status == 200) {
            getHttpRequest(url);
            document.getElementById("something").value = "";
        }
    };
    xmlhttp.send("value="+document.getElementById("something").value);
}

I guess the problem is the path, but how looks the modification of the code?