I have a site hosted at Google App Engine. Its current address is in the format like
xxx.appspot.com. Now I want someone to have access to it by typing some IP along with sub-directory, like
xxx.xxx.xxx.xxx/dir1/dir2/dir3. How can I do that?
This would be near-impossible to accomplish. It is easy to set up a GAE app on a custom domain, but it seems the OP has some more specific requirements.
Additionally, making it respond to a sub-path is not easy. If it is at all possible, it would involve altering your app, so that it basically ignores requests to anything but the desired sub-path.
However, I suspect you want to do this because you want to run other (non-GAE?) services on the same IP (that you own), while having your GAE app "installed" on the specified path. This is generally not possible. You might be able to work around it by setting up a web proxy on the desired path, which forwards all requests to the GAE app.