Struts1.1 handle /*.do/$VARIABLE_PATH/?attr=var

[NULL]

I have a requirement following.
The normal form for an action request is like this:
/ACTION.do?id=ID&attr=var,
now, I wish each ID has its own path.
So, I wish the request URL looks like this: /ACTION.do/$ID/?attr=var
The $ID is variable, so I can't map it one by one.

Either URL form /ACTION.do/$ID/?attr=var or /$ID/ACTION.do/?attr=var
is acceptable.
But I still not known how to configure struts-config.xml/web.xml or
write some Servlet to handle it.
Could anyone give me any help?
Thank.