i am not able to compare the string returned by the ajax request from servlet

Question

can anyone please help me with this? the first if statement works completely fine but the second if is never true meaning that whenever i print 'not' it is fine but when is print 'ok' it's not working and obviously if i use else with the first if then too it's not working

<script type="text/javascript">
    function signupfunction(){
        var name = document.getElementById('signupname').value;
        var email = document.getElementById('signupemail').value;
        var password = document.getElementById('signuppassword').value; 
        $.ajax({
            url : "AdminSignup?name=" + name + "&email=" + email + 
"&password=" + password + "",
            type : "GET",
            async : true,
            success : function(data) {
                if(data == 'not'){
                    alert("Email already exists");
                } 
                if(data == 'ok'){
                    alert('hello');
                }
            }
        });
    }
</script>

here is my doGet() function of servlet

protected void doGet(HttpServletRequest request, HttpServletResponse 
    response) throws ServletException, IOException {
        HttpSession session = request.getSession();
        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection con = 
                DriverManager.getConnection("jdbc:mysql://localhost/amazon? 
                user=root&password=test123");
            PreparedStatement statement = con.prepareStatement("select * from 
                sellers where email=?");
            statement.setString(1, request.getParameter("email"));
            ResultSet rs = statement.executeQuery();
            if(rs.next()) {
                response.getWriter().print("not");
            } else {
                PreparedStatement statement1 = con.prepareStatement("insert 
                    into sellers(email,password,name) values(?,?,?)");
                statement1.setString(1, request.getParameter("email"));
                statement1.setString(2, request.getParameter("password"));
                statement1.setString(3, request.getParameter("name"));
                statement1.executeUpdate();
                session.setAttribute("sessionAdminEmail", 
                    request.getParameter("email"));
                session.setAttribute("sessionAdminName", 
                    request.getParameter("name"));
                response.getWriter().print("ok");
            }
        } catch (Exception e) {

          }
    }

Answer 1

You are mixing up

response.getWriter().print("ok"); //this will not send your value to ajax

with:

response.getWriter().write("inserted new user");   //this will

Your Servlet:

protected void doGet(HttpServletRequest request, HttpServletResponse 
        response) throws ServletException, IOException {
            HttpSession session = request.getSession();
            response.setContentType("text/plain");  // Set content type of the response so that jQuery knows what it can expect.
            response.setCharacterEncoding("UTF-8"); // You want world domination, huh?
 try {


        Class.forName("com.mysql.jdbc.Driver");
        Connection con = DriverManager.getConnection("jdbc:mysql://localhost/amazon?user=root&password=test123");

        PreparedStatement statement = con.prepareStatement("select * from sellers where email=?");
        statement.setString(1, request.getParameter("email"));
        ResultSet rs = statement.executeQuery();

        if(rs.next()) {
            //if the email exists in sellers, then this will always evaluate to true...
            //response.getWriter().print("not"); //print will not send your value back to ajax..
            response.getWriter().write("email exists");       // Write response body.
        } else {
            PreparedStatement statement1 = con.prepareStatement("insert into sellers(email,password,name) values(?,?,?)");
            statement1.setString(1, request.getParameter("email"));
            statement1.setString(2, request.getParameter("password"));
            statement1.setString(3, request.getParameter("name"));
            statement1.executeUpdate();
            session.setAttribute("sessionAdminEmail", request.getParameter("email"));
            session.setAttribute("sessionAdminName", request.getParameter("name"));
            //response.getWriter().print("ok"); print will not send your value back to ajax
            response.getWriter().write("inserted new user");       // Write response body.
        }
    } catch (Exception e) {

      }
}

Also worth mentioning that == is not the same as ===. Use === in this case, it is the comparison operator you're looking for. Check out this for an explanation about the difference

<script type="text/javascript">
    function signupfunction(){
        var name = document.getElementById('signupname').value;
        var email = document.getElementById('signupemail').value;
        var password = document.getElementById('signuppassword').value; 
        $.ajax({
            url : "AdminSignup?name=" + name + "&email=" + email + 
"&password=" + password + "",
            type : "GET",
            async : true,
            success : function(data) {
                if(data === 'email exists'){
                    alert("Email already exists");
                } 
                if(data === 'inserted new user'){
                    alert('new user');
                }
            }
        });
    }
</script>

Check out this answer also, it gives a great explanation on how to use Ajax with Servlets. (much easier than the way you're currently doing it)

How to use Servlets and Ajax?