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:

• unmodifiableMultiValuedMap(MultiValuedMap)
• transformedMultiValuedMap(MultiValuedMap, Transformer, Transformer)

Since:

4.1

Field Summary

Fields

Modifier and Type	Field and Description
static MultiValuedMap	EMPTY_MULTI_VALUED_MAP An empty UnmodifiableMultiValuedMap.

Method Summary

Modifier and Type	Method and Description
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.
static <K,V> MultiValuedMap<K,V>	emptyMultiValuedMap() Returns immutable EMPTY_MULTI_VALUED_MAP with generic type safety.
static <K,V> Collection<V>	getCollection(MultiValuedMap<K,V> map, K key) Gets a Collection from MultiValuedMap in a null-safe manner.
static <K,V> Bag<V>	getValuesAsBag(MultiValuedMap<K,V> map, K key) Gets a Bag from MultiValuedMap in a null-safe manner.
static <K,V> List<V>	getValuesAsList(MultiValuedMap<K,V> map, K key) Gets a List from MultiValuedMap in a null-safe manner.
static <K,V> Set<V>	getValuesAsSet(MultiValuedMap<K,V> map, K key) Gets a Set from MultiValuedMap in a null-safe manner.
static boolean	isEmpty(MultiValuedMap<?,?> map) Null-safe check if the specified MultiValuedMap is empty.
static <K,V> ListValuedMap<K,V>	newListValuedHashMap() Creates a ListValuedMap with an ArrayList as collection class to store the values mapped to a key.
static <K,V> SetValuedMap<K,V>	newSetValuedHashMap() Creates a SetValuedMap with an HashSet as collection class to store the values mapped to a key.
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.
static <K,V> MultiValuedMap<K,V>	unmodifiableMultiValuedMap(MultiValuedMap<? extends K,? extends V> map) Returns an UnmodifiableMultiValuedMap backed by the given map.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

EMPTY_MULTI_VALUED_MAP

public static final MultiValuedMap EMPTY_MULTI_VALUED_MAP

An empty UnmodifiableMultiValuedMap.

Method Detail

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

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

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

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

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

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

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

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

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 behaviour, 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