if (rc.size() == 0) {
throw new BuildException(
"Cannot perform operation from directory to file.");
} else if (rc.size() == 1) {
Resource res = (Resource) rc.iterator().next();
FileProvider r = (FileProvider) res.as(FileProvider.class);
if (file == null) {
file = r.getFile();
rcs.removeElementAt(0);
} else {
throw new BuildException(
"Cannot concatenate multiple files into a single file.");
}