Simple AJAX query what I'm missing?

Using Ajax after an year...please tell me what I'm missing:

JSP/Ajax File

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <html>
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
    <title>Insert title here</title>
    <script type="text/javascript">
     
    function login() {
    var xmlhttp;
    var username = document.getElementById('username').value;
    var queryString = "username="+username;
    if(window.XMLHttpRequest){
    xmlhttp = new XMLHttpRequest();
    }else{
    xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
    }
    xmlhttp.open("GET", "LoginServlet", true);
    xmlhttp.setRequestHeader("Content-type","application/x-www-form-urlencoded");
    alert(queryString);
    xmlhttp.send(queryString);
    xmlhttp.onreadystatechange = function(){
    if(xmlhttp.readyState == 4 && xmlhttp.status == 200){
    alert(xmlhttp.responseText);
    }
    };
    }
    </script>
    </head>
    <body>
    <input type="text" name="username" id="username" />
    <input type="button" onclick="javascript:login()" value="login" />
    </body>
    </html>

Servlet:

package Servlets;
     
    import java.io.IOException;
    import java.io.PrintWriter;
     
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
     
    @WebServlet("/LoginServlet")
    public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
     
     
    public LoginServlet() {
    super();
     
    }
     
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    System.out.println("Servlet Called");
    PrintWriter out = response.getWriter();
    response.setContentType("text/html");
     
    String queryString = request.getParameter("username").toString();
    out.println(queryString);
    }
     
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    }
     
    }

I'm getting a null pointer exception in Servlet at line 27:

Probably the way I'm using xmlhttp.send(queryString); in JavaScript is wrong, but not able to figure out.

If you're using GET, don't you need to embed the query string in the URL?

I believe you use the "send(queryString)" function when you're doing a POST. Similarly, the "application/x-www-form-urlencoded" content-type is only needed when sending POST data.

Try:

Pete Nelson wrote:If you're using GET, don't you need to embed the query string in the URL?

I believe you use the "send(queryString)" function when you're doing a POST. Similarly, the "application/x-www-form-urlencoded" content-type is only needed when sending POST data.

Try:
xmlhttp.open("GET", "LoginServlet" + "?" + queryString, true); alert(queryString); xmlhttp.onreadystatechange = function(){ ...

Even if I'm using POST, it is giving the same error.
--EDIT... GOT it done...thanks

you should set onreadystate BEFORE you send it!

Eric

You should be using jQuery to avoid these types of issues in the first place.