Wicket 1.5–Custom Exception Page

I’m building a web application using Wicket for the first time (which is really cool by the way). I’d like that all uncaught RuntimeExceptions are displayed in a custom exception page which permit the user to submit the error report to myself.

I had no luck searching for a simple example that explains how to redirect a user to a custom page when an exception happens. (at least not for Wicket v1.5).

Following the description in the Wicket Migration Guide I came out with my own own code.

1) You have to add an AbstractRequestCycleListener to your WebApplication constructor and override the onException method.

public class TestApplication extends WebApplication {

  /**
   * Constructor
   */
  public TestApplication() {
	  
	  // In case of unhandled exception redirect it to a custom page
	  this.getRequestCycleListeners().add(new AbstractRequestCycleListener() {
		  @Override
	      public IRequestHandler onException(RequestCycle cycle, Exception e) {
			  return new RenderPageRequestHandler(new PageProvider(new ExceptionPage(e)));
		  }
	  });
  }

  public Class<HomePage> getHomePage() {
    return HomePage.class;
  }

}

2) Prepare the exception page, in my case I would like to fill out a form automatically with all exception information's (like full stacktrace) and let the user submit it.

My ExceptionPage.java looks like this:

public class ExceptionPage extends WebPage {

	private static final long serialVersionUID = 593717625018028083L;

	// My model for the form data
	FormExceptionProvider formProvider;
	
	// Mapped wicket:id 
	private static final String wicketIdformSendException="formSendException";
	private static final String wicketIdformTarget="formTarget";
	private static final String wicketIdformComments="formComments";
	private static final String wicketIdmessageDetails="messageDetails";
	private static final String wicketIdsubmitForm="submitForm";

	public ExceptionPage(Exception e) {
		formProvider = new FormExceptionProvider();
		formProvider.setTarget("Administrator");
		formProvider.setComments("Please provide here any useful information...");
		StringBuilder sb = new StringBuilder();
		sb.append(e.getClass().toString()+"\n");
		// Get the full stacktrace from exception and append to the string
		// Thanks to ripper234 (ref: http://stackoverflow.com/questions/1292858/getting-full-string-stack-trace-including-inner-exception)
		sb.append(joinStackTrace(e));
		// Add fullstacktrace as a form's field (readonly)
		formProvider.setAdditional(sb.toString());
		add(makeExceptionForm());
	}

	private Form<?> makeExceptionForm() {

		Form<?> form = new Form<Void>(wicketIdformSendException);

		FormComponent<?> tfTarget = new TextField<String>(
				wicketIdformTarget, new PropertyModel<String>(
						formProvider, "target"));
		form.add(tfTarget);
	
		FormComponent<?> taComments = new TextArea<String>(wicketIdformComments, new PropertyModel<String>(formProvider, "comments"));
		form.add(taComments);

		FormComponent<?> taAdditional = new TextArea<String>(wicketIdmessageDetails, new PropertyModel<String>(formProvider, "additional"));
		form.add(taAdditional);

		form.add(new Button(wicketIdsubmitForm) {
			private static final long serialVersionUID = -3553700128326728526L;

			@Override
			public void onSubmit() {
				/* 
				 * Do your stuff here (i.e. Send Email)
				 */
			}
		});
		return form;
	}
	
	public static String joinStackTrace(Throwable e) {
	    StringWriter writer = null;
	    try {
	        writer = new StringWriter();
	        joinStackTrace(e, writer);
	        return writer.toString();
	    }
	    finally {
	        if (writer != null)
	            try {
	                writer.close();
	            } catch (IOException e1) {
	                // ignore
	            }
	    }
	}

	public static void joinStackTrace(Throwable e, StringWriter writer) {
	    PrintWriter printer = null;
	    try {
	        printer = new PrintWriter(writer);

	        while (e != null) {

	            printer.println(e);
	            StackTraceElement[] trace = e.getStackTrace();
	            for (int i = 0; i < trace.length; i++)
	                printer.println("\tat " + trace[i]);

	            e = e.getCause();
	            if (e != null)
	                printer.println("Caused by:\r\n");
	        }
	    }
	    finally {
	        if (printer != null)
	            printer.close();
	    }
	}
}

And the related HTML code:

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Exception Page</title>
</head>
<body>
<form wicket:id="formSendException">
	<table>
	  <tr>
	    <td width="100" align="right" >Target</td>
	    <td><input wicket:id="formTarget" type="text" size="20" value="admin@unizh.ch"  readonly="readonly"/></td>
	  </tr>
	  <tr>
	   <td width="100" align="right" >Comments:</td>
	    <td><textarea wicket:id="formComments" rows="10" cols="50"></textarea></td>
	  </tr>
	  <tr>
	   <td width="100" align="right" >Additional:</td>
	   <td><textarea wicket:id="messageDetails" rows="20" cols="100" readonly="readonly"></textarea></td>
	   </tr>
	  <tr>
	    <td>&nbsp;</td>
	    <td align="left"><button wicket:id="submitForm" type="submit">Submit Report</button></td>
	    <td>&nbsp;</td>
	  </tr>
	</table>
</form>
</body>
</html>

I didn’t cared much (yet) about the UI, I was just looking to build something quick and useful for submitting error reports. An example of the resulting page is shown here:

Hope it helps!