On Servlet 3.0 or newer you could just specify
<web-app ...>
<error-page>
<location>/general-error.html</location>
</error-page>
</web-app>
But as you’re still on Servlet 2.5, there’s no other way than specifying every common HTTP error individually. You need to figure which HTTP errors the enduser could possibly face. On a barebones webapp with for example the usage of HTTP authentication, having a disabled directory listing, using custom servlets and code which can possibly throw unhandled exceptions or does not have all methods implemented, then you’d like to set it for HTTP errors 401, 403, 500 and 503 respectively.
<error-page>
<!-- Missing login -->
<error-code>401</error-code>
<location>/general-error.html</location>
</error-page>
<error-page>
<!-- Forbidden directory listing -->
<error-code>403</error-code>
<location>/general-error.html</location>
</error-page>
<error-page>
<!-- Missing resource -->
<error-code>404</error-code>
<location>/Error404.html</location>
</error-page>
<error-page>
<!-- Uncaught exception -->
<error-code>500</error-code>
<location>/general-error.html</location>
</error-page>
<error-page>
<!-- Unsupported servlet method -->
<error-code>503</error-code>
<location>/general-error.html</location>
</error-page>
That should cover the most common ones.
