MapEntryUtils unroll map entry (java)

MapEntryUtils.java

/**
 * Public Domain
 * 2023-10-19 Mike Pomraning, first version
 */
package local;

import java.util.Map;
import java.util.AbstractMap.SimpleEntry;
import java.util.AbstractMap.SimpleImmutableEntry;

import java.util.stream.Stream;
import java.util.Collection;

public class MapEntryUtils {
  /**
   * Unroll a possibly multi-value map entry into a stream of single-value map entries.
   * { key:[v1, v2] } -> [ {key:v1}, {key:v2} ]
   * { key:scalar } -> [ {key:scalar} ]
   *
   * E.g., myMap.entrySet().stream().flatMap(MapEntryUtils::unroll)...
   */
  public static <K> Stream<Map.Entry<K,Object>> unroll(Map.Entry<K,Object> entry) {
    //return (entry.getValue() instanceof Collection)
    //        ? ((Collection<Object>)entry.getValue()).stream().map(value -> new SimpleEntry<>(entry.getKey(), value))
    //        : Stream.of(entry);
    final Stream<Map.Entry<K,Object>> ret;
    final Object value = entry.getValue();

    if (value instanceof Collection) {
      final K key = entry.getKey();
      @SuppressWarnings("unchecked") final Collection<Object> values = (Collection<Object>) value;
      ret = values
              .stream()
              .map(val -> new SimpleEntry<>(key, val));
    } else {
      ret = Stream.of(entry);
    }

    return ret;
  }

  public static <K> Stream<SimpleImmutableEntry<K,Object>> unrollImmutable(Map.Entry<K,Object> entry) {
    final Stream<SimpleImmutableEntry<K,Object>> ret;
    final Object value = entry.getValue();

    if (value instanceof Collection) {
      final K key = entry.getKey();
      @SuppressWarnings("unchecked") final Collection<Object> values = (Collection<Object>) value;
      ret = values
              .stream()
              .map(val -> new SimpleImmutableEntry<>(key, val));
    } else {
      ret = Stream.of(new SimpleImmutableEntry<>(entry));
    }

    return ret;
  }

}