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.