I tried out Cayenne ROP on Android and this is what I found: it doesn't work out of the box, but it can be made to work with a bit of effort.
The Hessian library refers to a few classes that are not present in Android:
Cayenne itself refers to a few other classes missing in Android:
So references to these need to be dealt with. Here is what I did:
1) Use the existing open source"hessdroid" library instead of the regular hessian library
2) Remove reference to java.rmi.Remote from org.apache.cayenne.remote.RemoteService
3) Change RemoteException to IOException in org.apache.cayenne.remote.RemoteService
4) Use the java.beans code from Apache Harmony repackaged as com.googlecode.openbeans. I created the "openbeans" project on Google Code to host this code.
Only the cayenne-client library needs to be changed in this way. The server can stay the same, but it needs to have access to the openbeans library so that those classes are defined.
With these changes I was able to run the ROP client tutorial code in an Android app. I've attached the patch so you can see exactly what was needed. I don't know what the proper course of action would be to integrate something like this; presumably these aren't the kind of changes you would want to make to the core library, just to an android-only version. So maybe you have an idea.
I've attached the patch and the example project.