And you want this done from the runtime? Not sure if that's even possible. The only location I know of that you can reach is the /resource folder in your project folder, with the java actions supplied by CommunityCommons.
Folders inside Mendix deployment directory are usually locked for writing (I guess also for reading, but havnt tried yet).
The only folder where you can do these kind of actions is TEMP directory (\deployment\data\tmp).
Problem with this folder is, when deploying in cloud, Mendix would always delete the folder for every deployment.
So the unzipped files wont be there for the next deployment.
If you really need those files temporarily use the temp directory and unzipping can be done using simple java action (not sure if one already exists in commons)