Package org.apache.commons.collections4

Class MultiMapUtils

java.lang.Object
org.apache.commons.collections4.MultiMapUtils
public class MultiMapUtils extends Object
Provides utility methods and decorators for MultiValuedMap instances.

It contains various type safe and null safe methods. Additionally, it provides the following decorators:

Since:
4.1

  • Field Details

  • Method Details

    • emptyIfNull

      public static <K, V> MultiValuedMap<K,V> emptyIfNull(MultiValuedMap<K,V> map)
      Returns an immutable empty MultiValuedMap if the argument is null, or the argument itself otherwise.
      Type Parameters:
      K - the type of key in the map
      V - the type of value in the map
      Parameters:
      map - the map, may be null
      Returns:
      an empty MultiValuedMap if the argument is null

    • emptyMultiValuedMap

      public static <K, V> MultiValuedMap<K,V> emptyMultiValuedMap()
      Returns immutable EMPTY_MULTI_VALUED_MAP with generic type safety.
      Type Parameters:
      K - the type of key in the map
      V - the type of value in the map
      Returns:
      immutable and empty MultiValuedMap

    • getCollection

      public static <K, V> Collection<V> getCollection(MultiValuedMap<K,V> map, K key)
      Gets a Collection from MultiValuedMap in a null-safe manner.
      Type Parameters:
      K - the key type
      V - the value type
      Parameters:
      map - the MultiValuedMap to use
      key - the key to look up
      Returns:
      the Collection in the MultiValuedMap, or null if input map is null

    • getValuesAsBag

      public static <K, V> Bag<V> getValuesAsBag(MultiValuedMap<K,V> map, K key)
      Gets a Bag from MultiValuedMap in a null-safe manner.
      Type Parameters:
      K - the key type
      V - the value type
      Parameters:
      map - the MultiValuedMap to use
      key - the key to look up
      Returns:
      the Collection in the MultiValuedMap as Bag, or null if input map is null

    • getValuesAsList

      public static <K, V> List<V> getValuesAsList(MultiValuedMap<K,V> map, K key)
      Gets a List from MultiValuedMap in a null-safe manner.
      Type Parameters:
      K - the key type
      V - the value type
      Parameters:
      map - the MultiValuedMap to use
      key - the key to look up
      Returns:
      the Collection in the MultiValuedMap as List, or null if input map is null

    • getValuesAsSet

      public static <K, V> Set<V> getValuesAsSet(MultiValuedMap<K,V> map, K key)
      Gets a Set from MultiValuedMap in a null-safe manner.
      Type Parameters:
      K - the key type
      V - the value type
      Parameters:
      map - the MultiValuedMap to use
      key - the key to look up
      Returns:
      the Collection in the MultiValuedMap as Set, or null if input map is null

    • isEmpty

      public static boolean isEmpty(MultiValuedMap<?,?> map)
      Null-safe check if the specified MultiValuedMap is empty.

      If the provided map is null, returns true.

      Parameters:
      map - the map to check, may be null
      Returns:
      true if the map is empty or null

    • newListValuedHashMap

      public static <K, V> ListValuedMap<K,V> newListValuedHashMap()
      Creates a ListValuedMap with an ArrayList as collection class to store the values mapped to a key.
      Type Parameters:
      K - the key type
      V - the value type
      Returns:
      a new ListValuedMap

    • newSetValuedHashMap

      public static <K, V> SetValuedMap<K,V> newSetValuedHashMap()
      Creates a SetValuedMap with an HashSet as collection class to store the values mapped to a key.
      Type Parameters:
      K - the key type
      V - the value type
      Returns:
      a new SetValuedMap

    • transformedMultiValuedMap

      public static <K, V> MultiValuedMap<K,V> transformedMultiValuedMap(MultiValuedMap<K,V> map, Transformer<? super K,? extends K> keyTransformer, Transformer<? super V,? extends V> valueTransformer)
      Returns a TransformedMultiValuedMap backed by the given map.

      This method returns a new MultiValuedMap (decorating the specified map) that will transform any new entries added to it. Existing entries in the specified map will not be transformed. If you want that behavior, see TransformedMultiValuedMap.transformedMap(org.apache.commons.collections4.MultiValuedMap<K, V>, org.apache.commons.collections4.Transformer<? super K, ? extends K>, org.apache.commons.collections4.Transformer<? super V, ? extends V>).

      Each object is passed through the transformers as it is added to the Map. It is important not to use the original map after invoking this method, as it is a back door for adding untransformed objects.

      If there are any elements already in the map being decorated, they are NOT transformed.

      Type Parameters:
      K - the key type
      V - the value type
      Parameters:
      map - the MultiValuedMap to transform, must not be null, typically empty
      keyTransformer - the transformer for the map keys, null means no transformation
      valueTransformer - the transformer for the map values, null means no transformation
      Returns:
      a transformed MultiValuedMap backed by the given map
      Throws:
      NullPointerException - if map is null

    • unmodifiableMultiValuedMap

      public static <K, V> MultiValuedMap<K,V> unmodifiableMultiValuedMap(MultiValuedMap<? extends K,? extends V> map)
      Returns an UnmodifiableMultiValuedMap backed by the given map.
      Type Parameters:
      K - the key type
      V - the value type
      Parameters:
      map - the MultiValuedMap to decorate, must not be null
      Returns:
      an unmodifiable MultiValuedMap backed by the provided map
      Throws:
      NullPointerException - if map is null