org.apache.commons.collections4.map
Class MultiValueMap<K,V>

java.lang.Object
  org.apache.commons.collections4.map.AbstractIterableMap<K,V>
      org.apache.commons.collections4.map.AbstractMapDecorator<K,Object>
          org.apache.commons.collections4.map.MultiValueMap<K,V>

All Implemented Interfaces:

Serializable, Map<K,Object>, Get<K,Object>, IterableGet<K,Object>, IterableMap<K,Object>, MultiMap<K,V>, Put<K,Object>

public class MultiValueMap<K,V>
extends AbstractMapDecorator<K,Object>
implements MultiMap<K,V>, Serializable

A MultiValueMap decorates another map, allowing it to have more than one value for a key.

A MultiMap is a Map with slightly different semantics. Putting a value into the map will add the value to a Collection at that key. Getting a value will return a Collection, holding all the values put to that key.

This implementation is a decorator, allowing any Map implementation to be used as the base.

In addition, this implementation allows the type of collection used for the values to be controlled. By default, an ArrayList is used, however a Class to instantiate may be specified, or a factory that returns a Collection instance.

Note that MultiValueMap is not synchronized and is not thread-safe. If you wish to use this map from multiple threads concurrently, you must use appropriate synchronization. This class may throw exceptions when accessed by concurrent threads without synchronization.

Since:

3.2

Version:

$Id: MultiValueMap.java 1479407 2013-05-05 22:07:53Z tn $

See Also:

Serialized Form

MultiValueMap

public MultiValueMap()

Creates a MultiValueMap based on a HashMap and storing the multiple values in an ArrayList.

MultiValueMap

protected MultiValueMap(Map<K,? super C> map,
                        Factory<C> collectionFactory)

Creates a MultiValueMap which decorates the given map and creates the value collections using the supplied collectionFactory.

Type Parameters:

C - the collection class type

Parameters:

map - the map to decorate

collectionFactory - the collection factory which must return a Collection instance

multiValueMap

public static <K,V> MultiValueMap<K,V> multiValueMap(Map<K,? super Collection<V>> map)

Creates a map which wraps the given map and maps keys to ArrayLists.

Type Parameters:

K - the key type

V - the value type

Parameters:

map - the map to wrap

Returns:

a new multi-value map

Since:

4.0

multiValueMap

public static <K,V,C extends Collection<V>> MultiValueMap<K,V> multiValueMap(Map<K,? super C> map,
                                                                             Class<C> collectionClass)

Creates a map which decorates the given map and maps keys to collections of type collectionClass.

Type Parameters:

K - the key type

V - the value type

C - the collection class type

Parameters:

map - the map to wrap

collectionClass - the type of the collection class

Returns:

a new multi-value map

Since:

4.0

multiValueMap

public static <K,V,C extends Collection<V>> MultiValueMap<K,V> multiValueMap(Map<K,? super C> map,
                                                                             Factory<C> collectionFactory)

Creates a map which decorates the given map and creates the value collections using the supplied collectionFactory.

Type Parameters:

K - the key type

V - the value type

C - the collection class type

Parameters:

map - the map to decorate

collectionFactory - the collection factory (must return a Collection object).

Returns:

a new multi-value map

Since:

4.0

clear

public void clear()

Clear the map.

Specified by:

clear in interface Map<K,Object>

Specified by:

clear in interface Put<K,Object>

Overrides:

clear in class AbstractMapDecorator<K,Object>

See Also:

Map.clear()

remove

public V remove(Object key,
                Object value)

Removes a specific value from map.

The item is removed from the collection mapped to the specified key. Other values attached to that key are unaffected.

If the last value for a key is removed, null will be returned from a subsequent get(key).

Specified by:

remove in interface MultiMap<K,V>

Parameters:

key - the key to remove from

value - the value to remove

Returns:

the value removed (which was passed in), null if nothing removed

containsValue

public boolean containsValue(Object value)

Checks whether the map contains the value specified.

This checks all collections against all keys for the value, and thus could be slow.

Specified by:

containsValue in interface Map<K,Object>

Specified by:

containsValue in interface Get<K,Object>

Specified by:

containsValue in interface MultiMap<K,V>

Overrides:

containsValue in class AbstractMapDecorator<K,Object>

Parameters:

value - the value to search for

Returns:

true if the map contains the value

See Also:

Map.containsValue(Object)

put

public Object put(K key,
                  Object value)

Adds the value to the collection associated with the specified key.

Unlike a normal Map the previous value is not replaced. Instead the new value is added to the collection stored against the key.

Specified by:

put in interface Map<K,Object>

Specified by:

put in interface MultiMap<K,V>

Specified by:

put in interface Put<K,Object>

Overrides:

put in class AbstractMapDecorator<K,Object>

Parameters:

key - the key to store against

value - the value to add to the collection at the key

Returns:

the value added if the map changed and null if the map did not change

See Also:

Map.put(Object, Object)

putAll

public void putAll(Map<? extends K,?> map)

Override superclass to ensure that MultiMap instances are correctly handled.

If you call this method with a normal map, each entry is added using put(Object,Object). If you call this method with a multi map, each entry is added using putAll(Object,Collection).

Specified by:

putAll in interface Map<K,Object>

Specified by:

putAll in interface Put<K,Object>

Overrides:

putAll in class AbstractMapDecorator<K,Object>

Parameters:

map - the map to copy (either a normal or multi map)

See Also:

Map.putAll(Map)

entrySet

public Set<Map.Entry<K,Object>> entrySet()

NOTE: the returned Entry objects will contain as value a Collection of all values that are mapped to the given key. To get a "flattened" version of all mappings contained in this map, use iterator().

Specified by:

entrySet in interface Map<K,Object>

Specified by:

entrySet in interface Get<K,Object>

Overrides:

entrySet in class AbstractMapDecorator<K,Object>

See Also:

iterator()

values

public Collection<Object> values()

Gets a collection containing all the values in the map.

This returns a collection containing the combination of values from all keys.

Specified by:

values in interface Map<K,Object>

Specified by:

values in interface Get<K,Object>

Specified by:

values in interface MultiMap<K,V>

Overrides:

values in class AbstractMapDecorator<K,Object>

Returns:

a collection view of the values contained in this map

See Also:

Map.values()

containsValue

public boolean containsValue(Object key,
                             Object value)

Checks whether the collection at the specified key contains the value.

Parameters:

key - the key to search for

value - the value to search for

Returns:

true if the map contains the value

getCollection

public Collection<V> getCollection(Object key)

Gets the collection mapped to the specified key. This method is a convenience method to typecast the result of get(key).

Parameters:

key - the key to retrieve

Returns:

the collection mapped to the key, null if no mapping

size

public int size(Object key)

Gets the size of the collection mapped to the specified key.

Parameters:

key - the key to get size for

Returns:

the size of the collection at the key, zero if key not in map

putAll

public boolean putAll(K key,
                      Collection<V> values)

Adds a collection of values to the collection associated with the specified key.

Parameters:

key - the key to store against

values - the values to add to the collection at the key, null ignored

Returns:

true if this map changed

iterator

public Iterator<V> iterator(Object key)

Gets an iterator for the collection mapped to the specified key.

Parameters:

key - the key to get an iterator for

Returns:

the iterator of the collection at the key, empty iterator if key not in map

iterator

public Iterator<Map.Entry<K,V>> iterator()

Gets an iterator for all mappings stored in this MultiValueMap.

The iterator will return multiple Entry objects with the same key if there are multiple values mapped to this key.

NOTE: calling Map.Entry.setValue(Object) on any of the returned elements will result in a UnsupportedOperationException.

Returns:

the iterator of all mappings in this map

Since:

4.0

totalSize

public int totalSize()

Gets the total size of the map by counting all the values.

Returns:

the total size of the map counting all values

createCollection

protected Collection<V> createCollection(int size)

Creates a new instance of the map value Collection container using the factory.

This method can be overridden to perform your own processing instead of using the factory.

Parameters:

size - the collection size that is about to be added

Returns:

the new collection