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"
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "">
<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;
			xmlhttp = new XMLHttpRequest();
			xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
		}"GET", "LoginServlet", true);
		xmlhttp.onreadystatechange = function(){
			if(xmlhttp.readyState == 4 && xmlhttp.status == 200){
	<input type="text" name="username" id="username" />
	<input type="button" onclick="javascript:login()" value="login" />


package Servlets;


import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class LoginServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
    public LoginServlet() {


	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		System.out.println("Servlet Called");
		PrintWriter out = response.getWriter();
		String queryString = request.getParameter("username").toString();

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub


Thank You

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I'd say you're missing an explanation of what the issue is.

I'd say you're missing an explanation of what the issue is.

haha yeah that is one...
Actually I'm getting a null pointer exception in Servlet at line 27:

String queryString = request.getParameter("username").toString();

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

delete line NO. 22 in jsp file ie xmlhttp.send(queryString);
as in get method u dont need this. This is reqd in POST method..
For passing parameter in get method use this"GET", "LoginServlet?username="+username", true);

replace line NO 19 with this and ur code will work.
Lemme know anymore issues

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