Question

How can I show some loading message when making request using <f:ajax>?

Answer 1

If you’re not already using a 3rd party component library which could already have a ready-made component for that, such as PrimeFaces with <p:ajaxStatus>, then you can use the JSF-provided JavaScript faces.ajax.addOnEvent() function (and eventually also faces.ajax.addOnError()) to hook a function on ajax events.

Here’s a basic kickoff example:

<script>
    faces.ajax.addOnEvent(function(data) {
        var ajaxstatus = data.status; // Can be "begin", "complete" and "success"
        var ajaxloader = document.getElementById("ajaxloader");

        switch (ajaxstatus) {
            case "begin": // This is called right before ajax request is been sent.
                ajaxloader.style.display = 'block';
                break;
    
            case "complete": // This is called right after ajax response is received.
                ajaxloader.style.display = 'none';
                break;
    
            case "success": // This is called when ajax response is successfully processed.
                // NOOP.
                break;
        }
    });
</script>

<img id="ajaxloader" src="ajaxloader.gif" style="display: none;" />

See also section 13.3.5.2 of the Jakarta Faces 4.0 specification:

13.3.5.2 Monitoring Events For All Ajax Requests

The JavaScript API provides the faces.ajax.addOnEvent function that can be used to register a JavaScript function
that will be notified when any Ajax request/response event occurs. Refer to Section 14.4 “Registering Callback
Functions” for more details. The faces.ajax.addOnEvent function accepts a JavaScript function argument that will be
notified when events occur during any Ajax request/response event cycle. The implementation must
ensure the JavaScript function that is registered must be called in accordance with the events outlined in
Section TABLE 14-3 “Events”.

Note: in case you’re still using JSF 3.0 or older, then use jsf.ajax namespace instead of faces.ajax as in jsf.ajax.addOnEvent(...).