One of the new features in Pentaho Data Integration 8.1 is the ability to directly connect to Google Drive. PDI uses the Virtual File System (VFS) which allows you to connect to a variety of file systems in a transparent way.
To do this, you first have to enable the Google Drive api in https://console.developers.google.com/apis/api/drive.googleapis.com/ and create a service account (with OAuth). Download and place the JSON key under <data-integration>/plugins/pentaho-googledrive-vfs/credentials (the name of the key has to be client_secret.json).
After restarting Spoon go to File -> Open URL, the Google Drive option should be visible.
When selecting google drive, Google will ask you to authenticate
After authenticating, an extra file will be saved under the 'credentials' folder, allowing you to connect without authenticating. You will be able to browse your Google Drive locations
Now you can directly open and save files under Google Drive, or use the googledrive:// prefix in input and output steps to directly access and store files.