Jspで
<script type="text/javascript">
    function VerifyUsername()
    {
        //alert("In Verify Method");
        var name=document.getElementById("username").value;
        //alert(name);
        var xmlhttp;
        if (window.XMLHttpRequest)
        {// code for IE7+, Firefox, Chrome, Opera, Safari
            xmlhttp=new XMLHttpRequest();
            //alert("http");
         }
        else
        {// code for IE6, IE5
            xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
            alert("http active");
        }
        xmlhttp.onreadystatechange=function()
        {
            //alert("in Function()");
            if (xmlhttp.readyState==4 && xmlhttp.status==200)
            {
                try
                {
                    //alert("In Try");
                    document.getElementById("errorpass").innerHTML=xmlhttp.responseText;
                    /*var response = xmlhttp.responseText;
                    alert(response);
                    if(response.toString()=='notmatch')
                    {
                        alert("Ok");
                        document.getElementById("errorpass").innerHTML ="OK";
                    }
                    if(response =='match')
                    {
                        alert("Not Ok");
                        document.getElementById("errorpass").innerHTML ="Take Other Name.";
                    }*/
                }
                catch(ex)
                {
                    alert("Exception in function "+ex);
                }
            }
        }
        //xmlhttp.open("POST","servlet/UsernamePresence_Serv?UserId"+name,true);
        xmlhttp.open("POST","servlet/UsernamePresence_Serv?"+name,true);
        var params = "UserId="+name;
        xmlhttp.setRequestHeader("Content-type","application/x-www-form-urlencoded");
        xmlhttp.setRequestHeader("Content-length", params.length);
        xmlhttp.setRequestHeader("Connection", "close"); 
        xmlhttp.send(params);
    }
</script>
サーブレットで
public void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html");
    PrintWriter out = response.getWriter();
    try
    {
        Session session=Hibernate_Class.sessionObject();
        String userID=null;
        userID = request.getParameter("UserId");
        login_model loginModel_Obj=new login_model();
        loginModel_Obj._Name=userID;
        System.out.print("at "+userID);
        boolean username_bool=Hibernate_Class.usernamePresence(loginModel_Obj, session);
        if (username_bool)
        {
            out.println("Username Present In Database");
        }
        else
        {
            out.println("Username Not Present In Database");
        }
    }
    finally{}
    out.close();
}