proxy repository is blocked

I added a proxy repository in nexus. When I update now in Routing, it failed. The repo url I added is https://raw.githubusercontent.com/dianping/cat/mvn-repo

I can access this url

https://raw.githubusercontent.com/dianping/cat/mvn-repo/org/unidal/maven/plugins/codegen/2.3.2/codegen-2.3.2.pom

I can't access this url

https://raw.githubusercontent.com/dianping/cat/mvn-repo

response 400: Invalid request

So. It's the repo server block nexus from update.

If I don't use mirror in maven setting, Maven update will work right.

Meanwhile, when I use nexus public repositores group as my mirror(I also added proxy repo to public repositories group), It just report Failure to find org.unidal.maven.plugins:codegen-maven-plugin:jar:2.3.2 in http://172.xxx/nexus/content/groups/public

How can I solve this problem?

And I guess the maven resolve flow is like:

1. maven resolve a dependency
2. find the dependency in local
3. find in repo manager
4. find in proxy repo.

As the full url like https://raw.githubusercontent.com/dianping/cat/mvn-repo/org/unidal/maven/plugins/codegen/2.3.2/codegen-2.3.2.pom can be access, repo manager could fetch the specific pom url, if my guess is right.

I wonder: Unlike maven central,which you can access its index or called file tree, this cat.repo you can only access its file but not its directory. So what's the diffenrence in maven? How to handle this?

EDIT

Because I've successed update not using <mirrorOf>*</mirrorOf>. My local repository already download these missing plugins in Nexus. So I follow the tips in Maven not using the local repo, and that missing plugin does not cause error again, but another artifact not found in nexus again.

I also do as maven missing artifact shows, by

Deleting maven-metadata*.xml and _*.repositories inside local

Still not working.