Servlet not returning html code to ajax - ajax

Question

I have one jsp where below ajax call is made to get some data from servlet which will return html table in response :
function searchStudent() {
var lname = document.getElementsByName("lname");
var fname = document.getElementsByName("fname");
var email = document.getElementsByName("email");
var submit = document.getElementById("search");
xmlhttp.onreadystatechange=useResponse;
xmlhttp.open("GET", "SearchUser?
submit="+submit+"&fname="+fname+"&lname="+lname+"&email"+email,
true);
xmlhttp.send(null);
}
function useResponse() {
alert(xmlhttp.status+" "+xmlhttp.readyState);
if (xmlhttp.readyState==4 && xmlhttp.status==200) {
alert("hi"+xmlHttp.responseText);
document.getElementById("demo").innerHTML=xmlhttp.responseText;
alert("hi"+xmlHttp.responseText);
}
}
Function 'searchStudent()' is called on a button click.
Below is the servlet doGet() method :
protected void doGet(HttpServletRequest request, HttpServletResponse
response) throws ServletException, IOException {
String fname="";
String lname="";
String email="";
String button="";
button = request.getParameter("submit");
db = new DbOperation();
HttpSession session = request.getSession();
session.removeAttribute("msg");
if(button!=null && button.equalsIgnoreCase("Search")){
fname=request.getParameter("fname")==null?"":request.getParameter("fname");
lname=request.getParameter("lname")==null?"":request.getParameter("lname");
email=request.getParameter("email")==null?"":request.getParameter("email");
Admin admin =(Admin) session.getAttribute("Admin");
int adminId=0;
if(admin!=null)
adminId=admin.getId();
ArrayList<Student> student = new ArrayList<Student>();
student= db.searchStudent(fname,lname,email,adminId);
PrintWriter pw = response.getWriter();
response.setContentType("text/html");
response.setHeader("Cache-Control", "no-cache");
if(student!=null && student.size()>0){
session.setAttribute("student", student);
StringBuilder std= new StringBuilder();
std.append("<table border='1'><th>Id</th><th>First_name</th><th>Last_Name</th><th>Email</th><th>State</th><th>City</th>");
for(Student st :student ){
std.append("<tr><td>"+st.getId()+"</td><td>"+st.getFname()+"</td><td>"+st.getLname()+"</td><td>"+st.getEmail()+"</td><td>"+st.getState()+"</td><td>"+st.getCity()+"</td></tr>");
}
std.append("<table>");
//pw.write(std.toString());
pw.write(std.toString());
//pw.write("<h3>here</h3>");
}else{
pw.write("<h3>Student doesn't exists</h3>");
/*RequestDispatcher rd = request.getRequestDispatcher("AdminServlet?msg1=Student doesn't exists");
rd.forward(request, response);*/
}
}
}
The html returned by servlet is directly displayed in console and not coming to the jsp from where ajax call is made.
alert("hi"+xmlHttp.responseText); is also not getting populates