Java POJO to dot notation

gistfile1.txt

public class FlattenedMapEntry {
    String key;
    String value;
}


public static List<FlattenedMapEntry> flattenMap(String parent, Map<?, ?> map) {
        List<FlattenedMapEntry> results = new ArrayList<>();

        for (Object o : map.entrySet()) {
            Map.Entry pair = (Map.Entry) o;
            String key;

            if (parent == null) {
                key = pair.getKey().toString();
            } else {
                key = parent + "." + pair.getKey().toString();
            }

            if (pair.getValue() instanceof Map<?, ?>) {
                results.addAll(flattenMap(key, (Map<?, ?>) pair.getValue()));
            } else if (pair.getValue() instanceof Set<?> || pair.getValue() instanceof List<?>) {
                List<?> list = (List<?>) pair.getValue();
                for (Object aList : list) {
                    if (aList instanceof Map<?, ?>) {
                        results.addAll(flattenMap(key, (Map<?, ?>) aList));
                    } else {
                        results.add(FlattenedMapEntry.builder().key(key + "." + aList.toString()).value("").build());
                    }
                }
            } else if (pair.getValue() != null) {
                String value = pair.getValue().toString();
                results.add(FlattenedMapEntry.builder().key(key).value(value).build());
            }
        }
        return results;
    }