Jennifer Grucza

Today, for the first time, I added AJAX (aka XMLHttpRequest) to a web application. (Well, it wasn’t actually AJAX, because I was making a synchronous request instead of an asynchronous one, but close enough.) I’ve known about the technique for just slightly longer than it has been dubbed “AJAX”, but never taken the time to figure out how to use it. Now that I know how to use it, I wish I had known about it years ago. This whole time (the 6 or so years I’ve been doing serious web development), I’ve been limping along with hacky solutions like refreshing an invisible frame, polling the server. Yuck. This makes so much more sense.

To make things somewhat easier for myself, I created a reusable javascript function to wrap the details of the XML call:

/*
    Sends a POST request to the server in the background and
    returns the result as XML or false if there was a problem
    sending the request.
*/
function synchronousPost(requestURL, parameterMap) {
    var requestBody = "";
    for (param in parameterMap) {
        if (requestBody != "") {
            requestBody += "&";
        }
        requestBody += param + "=" + parameterMap[param];
    }
	
    var xmlRequest;
    if (window.XMLHttpRequest) {
        xmlRequest = new XMLHttpRequest();
    } else if (window.ActiveXObject) {
        xmlRequest = new ActiveXObject("Microsoft.XMLHTTP");
    }
	
    if (xmlRequest) {
        xmlRequest.open("POST", requestURL, false);
        xmlRequest.setRequestHeader(
            "Content-Type",
            "application/x-www-form-urlencoded");
        xmlRequest.send(requestBody);
        if (xmlRequest.status == 200) {
            return xmlRequest.responseXML;
        }
    }
	
    return false;
}

Then in my java Struts action class on the server side, I just need to make sure to set the content type, write my xml directly out to the response, and return null for the ActionForward:

public ActionForward execute(
        ActionMapping mapping,
        ActionForm form,
        HttpServletRequest request,
        HttpServletResponse response) throws Exception {
	
    String xml = "<response>";
    xml += "success";
    xml += "</response>";
	
    response.setContentType("text/xml");
    response.getWriter().write(xml);
	
    return null;
}

Of course, you don’t need to use a Struts action class for this, but since all my code uses Struts, it’s easiest just to use the same framework.

I was pretty excited to get this to work - it’s a neat little technology, and it solved a little UI issue I was running into.

This entry was posted on Friday, July 29th, 2005 at 5:19 pm and is filed under Web Development, Java. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.