In WebLogic, there's a method to personalize standard error pages like HTTP 404 within the web programs using web.xml

<web-app xmlns="http://java.sun.com/xml/ns/j2ee">
    <error-page>
        <error-code>404</error-code>
        <location>errors/404.htm</location>
    </error-page>
</web-app>

It is possible to method to configure default domain-wide error page for the programs WebLogic has running without editing web.xml? Will it be easy to capture the 404 in Apache and serve a typical error page?

I'm not sure of a method to set the 404 page domain-wide (I doubt there's a means because this will probably be provided individually by each application).

However, you are able to catch it on the internet-tier. For Apache, you should use the ErrorDocument directive. For instance, ErrorDocument 404 /404.html

You can define a mistake page in Apache WebLogic wordpress plugin:

http://download.oracle.com/docs/cd/E12840_01/wls/docs103/plugins/apache.html