if (!(target instanceof FileSystemDataset)) {
throw new UnsupportedOperationException("Partitions only supported for " +
"FileSystemDataset. Dataset: " + target);
}
FileSystemDataset fsDataset = (FileSystemDataset) target;
PartitionKey key = fsDataset.keyFromDirectory(new Path(partitionDir));
if (key != null) {
working = fsDataset.getPartition(key, true);
}
return new DatasetRecordWriter<E>(working);
} else {