You can now optionally [...] intercept any error message sent back from the server, and perform custom client-side actions as a result [...]. (source)

Well, I disagree with “optionally”. As far as I understand, if you don’t explicitly intercept the error/exception sent back from the server from within an UpdatePanel, your user will get an unfriendly javascript error like this:

So what can you do to fix this? Easy, just add this piece of Javascript code to your Masterpage (or to any page if you don’t have/use a Masterpage):

<%-- This script must be placed after the form declaration (i.e. <form id="form1" runat="server">) --%>
<script type="text/javascript">
    Sys.Application.add_load(AppLoad);

    function AppLoad() {
        Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequest);
    }

    function EndRequest(sender, args) {
        // Check to see if there's an error on this request.
        if (args.get_error() != undefined) {

            var msg = args.get_error().message.replace("Sys.WebForms.PageRequestManagerServerErrorException: ", "");

            // Show the custom error.
            // Here you can be creative and do whatever you want
            // with the exception (i.e. call a modalpopup and show
            // a nicer error window). I will simply use 'alert'
            alert(msg);

            // Let the framework know that the error is handled,
            //  so it doesn't throw the JavaScript alert.
            args.set_errorHandled(true);
        }
    }
</script>

Now you should get error messages like this (javascript alert):

This is exactly how exceptions used to be displayed when thrown inside an UpdatePanel before .NET 3.5.

Note: I do understand the benefits of a the new approach. It gives you flexibility to present the error message any way you want, before your hands where quite tied to this simple Javascript alert window.

As a matter of fact, I’ve implemented a nice ModalPopup and have ensure that only user-friendly messages are actually shown: only messages of a certain type (i.e. UIMessageException) are forwarded to the user without any cleanup/transformation.

References:

• Exception handling best practices in ASP.NET web applications
• How Do I: Customize Error Handling for the ASP.NET AJAX UpdatePanel
• MVP blog: UpdatePanel: having fun with errors
• MSDN post (be careful, not 100% correct): Customizing Error Handling for ASP.NET UpdatePanel Controls

Cheers!

However, the real motivation behind this project is to keep me updated with latest trends in the Java/J2EE world. There are countless interesting Java frameworks and tools, but for this project I’ve picked the following winning set: JSF, Facelets, RichFaces, Spring and Hibernate!

So, this project does not have real schedules or documented requirements. It’s a fun and open project that is always there for me, just waiting to be updated the latest trends in java development! By the way, the current technologies in place for this version are:

• JSF 1.2 / Apache MyFaces 1.2.3
• Facelets 1.1.14
• RichFaces 3.2.1
• Spring Framework 2.5.5
• Hibernate 3
• HSQLDB 1.8.0
• JUnit 4.4

If you have any questions or would like to participate, just leave a comment here.