Don't worry about this problem, its easy. If you want to get all files and folder from specific FOLDER, then just copy and paste this code in your project and it will retrieve all the files and folder from the specific Folder.
Note: You should have your own Folder ID
List<File> result = new ArrayList<File>();
Files.List request = null;
try {
request = mService.files().list();//plz replace your FOLDER ID in below linez
FileList files = request.setQ("'"+MyFoler_Id+"'in parents and trashed=false").execute();
result.addAll(files.getItems());
request.setPageToken(files.getNextPageToken());
}
catch (IOException e)
{
System.out.println("An error occurred: " + e);
request.setPageToken(null);
}
//Print Out the Files and Folder Title which we have retrieved.
for(File f:result)
{
System.out.println("My recvd data "+f.getTitle());
}