Servlet对Javascript的响应以纯文本形式显示在浏览器上

Question

I have my servlet sending the following response to a JS ajax call:

            response.setContentType("text/plain");
            PrintWriter out = response.getWriter();
            out.print("start");
            out.close();

and the call from the web page has the following code:

function update() {
    var xmlhttp = new XMLHttpRequest();
    var id = '${user.id}';
    var height = (window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight);
    height = height-40;
    var params = "action=update&id=" + id + "&height=" + height;
    xmlhttp.open("POST", "/Anabasis/UserControl", true);
    xmlhttp.setRequestHeader("Content-type",
            "application/x-www-form-urlencoded");
    xmlhttp.setRequestHeader("Content-length", params.length);
    xmlhttp.onreadystatechange = function() {
        if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
            var answer = xmlhttp.responseText;
            if(answer=="start"){
                window.location.href = "/project/page1.jsp";
            } else {
                window.location.href = "/project/page2.jsp";
            }
        }
    };
    xmlhttp.send(params);
}
setTimeout(update, 10000);

If start is send back by the Servlet, the browser should be redirected to another page. This may be done without the user's doing anything since the JS request is send every 10 seconds.

Now the result is that I do not get the answer to page but just a black page with the text: "start"

Can anyone tell me what to add in order to asure that the answer gets back to the JS function?

Answer 1

It's better to forward your request according to your requirement, like:

RequestDispatcher rd=request.getRequestDispatcher("./project/page1.jsp");
rd.forward(request, response);

Answer 2

I have found the solution, sorry for the question. The code actually works fine, just in some case the Servlet gets not called by this update function but by another form from the same page. So of course the answer is not send to the function, explaining the misbehaviour.

Is there any guide on best practices concerning Servlet-Webpage communication? I guess I shall need that very much.