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How to get jQuery, AJAX and a servlet working together?
$(document).ready(function() {
        $("a").click(function(){
            alert("Should be going to servlet now");
            $.ajax({
                type: 'GET',
                url: "checkName",
                data: {userName: "Hexose"},
                success: function(data){ alert(data);}
            });
        });

    });

public class CheckUserNameServlet extends HttpServlet {

protected void doGet(HttpServletRequest request,
        HttpServletResponse response)
        throws ServletException, IOException {

    String targetUN = request.getParameter("userName");

    if (data.UserDB.userNameExists(targetUN)) {
        String exists = "Username already taken...";
        response.setContentType("text");
        response.setHeader("Cache-Control", "no-cache");
        response.getWriter().write(exists);
        response.setStatus(200);
    } else {
        response.getWriter().write("Username is available...");
    }
}

<tr>
  <td align="right">Username:</td>
  <td><input type="text" name="userName" id="userName" value="${user.userName}"  /</td>
  <td><span id="exist"> <a href="">Check Availability</a></span></td>
</tr>

$("#exist a").click(........

$("a").click(function(e){
    e.preventDefault();
    ...........

$("#userName").val()