Raible Designs

Using Struts' Declared Exceptions

With a little prodding from Erik Hatcher today, I took another look at Struts' Declared Exceptions feature. At the end of last year, I was wishing I could use declared exceptions to do chained exceptions for my Action classes. Basically, in each of my Actions, I have a try/catch wrapped around a call to the Business Delegate (example: UserAction.java). You'll notice that all the CRUD methods have the same catch block for exception handling:

} catch (Exception e) {
    e.printStackTrace();
    errors.add(ActionErrors.GLOBAL_ERROR,
               new ActionError("errors.general"));

    while (e != null) {
        errors.add(ActionErrors.GLOBAL_ERROR,
                   new ActionError("errors.detail", e.getMessage()));
        e = (Exception) e.getCause();
    }

    saveErrors(request, errors);

    return mapping.getInputForward();
}

After talking with Erik this morning, I decided to create an ActionExceptionHandler for java.lang.Exception. In my struts-config.xml, I added:

<exception type="java.lang.Exception" key="errors.general"
    handler="org.appfuse.webapp.action.ActionExceptionHandler"/>

I have "errors.general=The process did not complete. Details should follow." Here is the code for ActionExceptionHandler:

public final class ActionExceptionHandler extends ExceptionHandler {

    public ActionForward execute(Exception ex, ExceptionConfig ae,
                                 ActionMapping mapping,
                                 ActionForm formInstance,
                                 HttpServletRequest request,
                                 HttpServletResponse response)
      throws ServletException {
        ActionForward forward = null;
        ActionError error = null;
        ActionErrors errors = new ActionErrors();
        String property = null;

        // Build the forward from the exception mapping if it exists
        // or from the form input
        if (ae.getPath() != null) {
            forward = new ActionForward(ae.getPath());
        } else {
            forward = mapping.getInputForward();
        }

        ex.printStackTrace();
        errors.add(ActionErrors.GLOBAL_ERROR, new ActionError(error.getKey()));

        while (ex != null) {
            errors.add(ActionErrors.GLOBAL_ERROR,
                       new ActionError("errors.detail", ex.getMessage()));
            ex = (Exception) ex.getCause();
        }

        // Store the errors and exception
        request.setAttribute(Globals.ERROR_KEY, errors);

        return forward;
    }
}

This allows me to remove my generic try/catches from my action classes - very slick IMO (or at least better than the code smell I had)! Of course, I still have some catch blocks that catch specific exceptions, but I can either (1) leave those intact, or (2) create another declared exception for that particular action/exception. I dig it and will be adding it (in short order) to AppFuse.

Update (June 23, 2003): Here's a more thoroughly tested code sample of this same class.

Sending POJOs to the UI instead of ActionForms

I'm starting to think that my Struts-based apps could be simplified if I didn't convert POJOs to Action Forms when retrieving them from the database. By this, I mean to say that I'd like to retrieve and display POJOs on the UI, and then capture their information (as Action Forms) when saving the form. The reason I want to do this is because of Hibernate's Lazy Loading feature and formatting Dates. Basically, Hibernate allows you to load children of an object lazily (i.e. resumes of a User), when the getResumes() method is called. I've created [a page|POJOsToForms] on my wiki to explain further and continue this discussion. Of course, you can always leave comments here if you'd rather - they cross-reference each other. The [RollingWiki|http://www.rollerweblogger.org/wiki/Wiki.jsp?page=RollerWikiPlugin] rocks!

www.mail-archive.com

If you're doing development on an open source project, I recommend that you get your mailing list archived by mail-archive.com. It's pretty easy to setup and offers a nice google-like search interface. I recently added struts-apps, struts-menu-user and the display tag lists. I hope this makes it a lot easier for folks using these applications. I might even add Roller, but I figured Dave could handle that if he really wants it (it's already being done by gname anyway).

Either way, gname or mail-archive.com, if you're using a SourceForge mailing list, you'd better get a better archiving system b/c SourceForge's sucks! Why? No searching! What good is an archive without searching?!