@Override
    public BatchWriteItemOutcome batchWriteItemUnprocessed(
            Map<String, List<WriteRequest>> unprocessedItems) {
        return doBatchWriteItem(new BatchWriteItemSpec()
                .withUnprocessedItems(unprocessedItems));
    }
The implementation for <code>BatchWriteItemApi</code>.
aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/document/internal/BatchWriteItemImpl.java