Customizing Error Pages

AEM comes with a standard error handler for handling HTTP errors; for example, by showing:

Standard error message

To respond to errors, AEM provides a 404.jsp script under /libs/sling/servlet/errorhandler.

TIP

Because AEM is based on Apache Sling, further information is available in the Apache error handling documentation.

NOTE

On an author instance, CQ WCM Debug Filter is enabled by default. This always results in the response code 200. The default error handler responds by writing the full stack trace to the response.

On a publish instance, CQ WCM Debug Filter is always disabled (even if configured as enabled).

How to Customize Pages Shown by the Error Handler

You can develop your own scripts to customize the pages shown by the error handler when an error is encountered. To do this you will leverage AEM’s standard overlay mechanism so that your customized pages are created under /apps and overlay the default pages that are under /libs.

  1. In the repository, copy the default script(s):

    • from /libs/sling/servlet/errorhandler/
    • to /apps/sling/servlet/errorhandler/

    The destination path does not exist by default, so you will need to create it when doing this for the first time.

  2. Navigate to /apps/sling/servlet/errorhandler. Here you can either:

    • edit the appropriate existing script to supply the information required. Or
    • create, and edit, a new script for the required code.
  3. Save the changes and test.

CAUTION

The 404.jsp script has been specifically designed to cater to AEM authentication; in particular, to allow for system login in the case of these errors.

Therefore, replacement of this script should be done with great care.

Customizing the Response to HTTP 500 Errors

The HTTP 500 Internal Server Error indicates a server-side error such as the server encountering an unexpected condition which prevented it from fulfilling the request.

When request processing results in an exception, the Apache Sling framework (which AEM is built on):

  • Logs the exception
  • And returns in the body of the response:
    • The HTTP response code 500
    • The exception stack trace

By customizing the pages shown by the error handler a 500.jsp script can be created. However, it is only used if HttpServletResponse.sendError(500) is executed explicitly; i.e. from an exception catcher.

Otherwise, the response code is set to 500, but the 500.jsp script is not executed.

To handle 500 errors, the file name of the error handler script must be the same as the exception class (or superclass). To handle all such exceptions you can create a script /apps/sling/servlet/errorhandler/Throwable.jsp or /apps/sling/servlet/errorhandler/Exception.jsp.

CAUTION

On an author instance, CQ WCM Debug Filter is enabled by default. This always results in the response code 200. The default error handler responds by writing the full stack trace to the response.

For a custom error-handler, responses with code 500 are needed - so the CQ WCM Debug Filter needs to be disabled. This ensures that the response code 500 is returned, which in turn triggers the correct Sling error-handler.

On a publish instance, CQ WCM Debug Filter is always disabled (even if configured as enabled).

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