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

      @Deprecated public static <K, V> Bag<V> getValuesAsBag(MultiValuedMap<K,V> map, K key)
      Deprecated.
      Since 4.6.0, use getValuesAsMultiSet(MultiValuedMap, Object) instead.
      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:
      A new Bag containing the values from the MultiValuedMap, 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:
      A new List containing the values from the MultiValuedMap, or null if input map is null.

    • getValuesAsMultiSet

      public static <K, V> MultiSet<V> getValuesAsMultiSet(MultiValuedMap<K,V> map, K key)
      Gets a MultiSet 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:
      A new MultiSet containing the values from the MultiValuedMap, or null if input map is null.
      Since:
      4.6.0

    • 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:
      A new Set containing the values from the MultiValuedMap, or null if input map is null.

    • invert

      public static <K, V, M extends MultiValuedMap<K, V>> M invert(MultiValuedMap<? extends V,? extends K> input, M output)
      Inverts the mappings from an input MultiValuedMap by adding entries to an output MultiValuedMap. The input is unchanged.

      Use this method to have complete control of the output MultiValuedMap or when merging several inverse mappings. In simple cases, consider using MultiValuedMap.inverted() method.

      Type Parameters:
      K - the input value type and output key type.
      V - the input key type and output value type.
      M - the output MultiValuedMap type where K is the key type and V is the value type.
      Parameters:
      input - The input key-value mappings of type <V, K>.
      output - The output value-key mappings of type <K, V>.
      Returns:
      The updated output MultiValuedMap of type <K, V>
      Since:
      4.6.0
      See Also:

    • 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.