Ajax is a technology that enables a javascript program (embedded in a web page displayed by your browser) to communicate with a server and provide dynamic content.  This communication occurs “under the covers” and is, hopefully, “seamless.”  The masher’s getWebServiceResult uses Ajax to retrieve information from a commercial Web service.

function getWebServiceResult() {
    if (window.XMLHttpRequest) {// code for modern browsers
        request = new XMLHttpRequest();
    } else {// older versions of IE
        request = new ActiveXObject("Microsoft.request");
    }
    var url = "https://masher.cunyfirst.cuny.edu/proxy";
    request.open("GET", url, false); // false means synchronous operation
    request.send();
    if (request.readyState != 4 || request.status != 200) {
        alert("AJAX error: " + request.statusText + " (state=" + request.readyState + ", status=" + request.status + ")");
        return null;
    }
    return getSelectedItem(request.responseText);
}

Problem is, the masher page comes from from https://masher.cunyfirst.cuny.edu but the Web service is provided by http://outside-webservice.com. Access is prohibited by the “Same Origin Policy” which is especially restrictive for Ajax requests (though there are work-arounds).  So we “proxy” these requests through the masher’s web server.  getWebServiceResult connects to masher.cunyfirst.cuny.edu which relays requests for /proxy to outside-webservice.com.  As far as the browser is concerned, masher.html and the proxied page are in the same domain.  This approach also allows us to alter the request on its way to outside-webservice.com.  To add authentication information (outside-webservice requires a user name and password), for example.  And it allows a javascript routine in an SSL protected page (masher.html) to communicate with a non-SSL Web service.  All this for free, no programming required, just five lines of Apache configuration:

LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_http_module modules/mod_proxy_http.so

RequestHeader set Authorization "Basic authstring"
ProxyPass /proxy http://outside-webservice.com/
ProxyPassReverse /proxy http://outside-webservice.com/

Where authstring is base 64 encoded user:password.

The response from outside-webservice.com is an XML page that contains a collection of “items”:

<result count="3">
    <item id="item0">
        <select>false</select>
        <value>first value</select>
    </item>
    <item id="item1">
        <select>true</select>
        <value>second value</select>
    </item>
    <item id="item2">
        <select>false</select>
        <value>third value</select>
    </item>
</result>

We’re only interested in one. I found a convenient XML to JSON parser that made it easy to find it.

<script type="text/javascript" src="http://www.thomasfrank.se/downloadableJS/xml2json.js"></script>

function getSelectedItem(response) {
    var responseJson = xml2json.parser(response);
    var result = responseJson.result;
    var items = result.item;
    if (typeof items === 'undefined') { return null; }
    for (var i = 0; i < items.length; i++) {
        var item = items[i];
        if (item.select == 'true') {
            return item;
        }
    }
    return null;
}

This is sort of a “mashup” style of programming.  Rather than write my own parser (limited purpose and  designed for this XML document) I stole  Thomas Frank’s general purpose one.

Resources

Ross turned me on to this useful article about mashups.

I wrote several of my own proxies before settling on the Apache/mod_proxy approach. I really like Jersey. My colleague Vamsi Naidu introduced me to IBM’s
RPC Adapter (and here). Then there’s always Apache’s trusty HTTP Client.

I found a few interesting articles on javascript and PeopleCode

http://community.psoftpros.net/profiles/blogs/injecting-javascript-amp-ajax
http://hosteddocs.ittoolbox.com/VRM100804.pdf
http://greysparling.com/Blog/enhancing-the-usability-of-peoplesoft-applications
http://xtrahot.chili-mango.net/2005/08/peoplesoft-page-javascript-insertion
http://peoplesofttipster.com/2007/07/24/counting-characters-in-a-field