When an exception is thrown and travels to the top level of the servlet stack, apollo renders the exception traceback into HTML format for the browser. The programmer can then see the exception onscreen in their browser rather then reading through logs.

It should be noted that apollo only supports this as a possible configuration. Since the programmer controls the actions of the servlet, exceptions are only rendered to the browser if you configure your servlet similar to the demo application. Production systems may wish to shield end users from Java Stack traces appearing when an error occurs. It may be a good idea to allow your system to run in two modes, production and development. In production mode a predesigned error screen comes up, possibly with a customer service phone number, and an email is dispatched to engineering with the Stack Trace. In development mode, the exception is displayed in the browser so the programmer an immediately see the stack trace.