org.apache.commons.collections.map

Class MultiValueMap

java.lang.Object

org.apache.commons.collections.map.AbstractMapDecorator

org.apache.commons.collections.map.MultiValueMap

All Implemented Interfaces:

java.util.Map, MultiMap

public class MultiValueMap
extends AbstractMapDecorator
implements MultiMap

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:

Commons Collections 3.2

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map

java.util.Map.Entry<K,V>

Constructor Summary

Constructors

Constructor and Description
MultiValueMap() Creates a MultiValueMap based on a HashMap and storing the multiple values in an ArrayList.

Method Summary

Modifier and Type	Method and Description
void	clear() Clear the map.
boolean	containsValue(java.lang.Object value) Checks whether the map contains the value specified.
boolean	containsValue(java.lang.Object key, java.lang.Object value) Checks whether the collection at the specified key contains the value.
static MultiValueMap	decorate(java.util.Map map) Creates a map which wraps the given map and maps keys to ArrayLists.
static MultiValueMap	decorate(java.util.Map map, java.lang.Class collectionClass) Creates a map which decorates the given map and maps keys to collections of type collectionClass.
static MultiValueMap	decorate(java.util.Map map, Factory collectionFactory) Creates a map which decorates the given map and creates the value collections using the supplied collectionFactory.
java.util.Collection	getCollection(java.lang.Object key) Gets the collection mapped to the specified key.
java.util.Iterator	iterator(java.lang.Object key) Gets an iterator for the collection mapped to the specified key.
java.lang.Object	put(java.lang.Object key, java.lang.Object value) Adds the value to the collection associated with the specified key.
void	putAll(java.util.Map map) Override superclass to ensure that MultiMap instances are correctly handled.
boolean	putAll(java.lang.Object key, java.util.Collection values) Adds a collection of values to the collection associated with the specified key.
java.lang.Object	remove(java.lang.Object key, java.lang.Object value) Removes a specific value from map.
int	size(java.lang.Object key) Gets the size of the collection mapped to the specified key.
int	totalSize() Gets the total size of the map by counting all the values.
java.util.Collection	values() Gets a collection containing all the values in the map.

Methods inherited from class org.apache.commons.collections.map.AbstractMapDecorator

containsKey, entrySet, equals, get, hashCode, isEmpty, keySet, remove, size, toString

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface org.apache.commons.collections.MultiMap

get, remove, size

Methods inherited from interface java.util.Map

compute, computeIfAbsent, computeIfPresent, containsKey, entrySet, equals, forEach, getOrDefault, hashCode, isEmpty, keySet, merge, putIfAbsent, replace, replace, replaceAll

Constructor Detail

MultiValueMap

public MultiValueMap()

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

Method Detail

decorate

public static MultiValueMap decorate(java.util.Map map)

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

Parameters:

map - the map to wrap

decorate

public static MultiValueMap decorate(java.util.Map map,
                                     java.lang.Class collectionClass)

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

Parameters:

map - the map to wrap

collectionClass - the type of the collection class

decorate

public static MultiValueMap decorate(java.util.Map map,
                                     Factory collectionFactory)

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

Parameters:

map - the map to decorate

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

clear

public void clear()

Clear the map.

Specified by:

clear in interface java.util.Map

Overrides:

clear in class AbstractMapDecorator

remove

public java.lang.Object remove(java.lang.Object key,
                               java.lang.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 subsequant get(key).

Specified by:

remove in interface java.util.Map

Specified by:

remove in interface MultiMap

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(java.lang.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 java.util.Map

Specified by:

containsValue in interface MultiMap

Overrides:

containsValue in class AbstractMapDecorator

Parameters:

value - the value to search for

Returns:

true if the map contains the value

put

public java.lang.Object put(java.lang.Object key,
                            java.lang.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 java.util.Map

Specified by:

put in interface MultiMap

Overrides:

put in class AbstractMapDecorator

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

putAll

public void putAll(java.util.Map 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 java.util.Map

Overrides:

putAll in class AbstractMapDecorator

Parameters:

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

values

public java.util.Collection 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 java.util.Map

Specified by:

values in interface MultiMap

Overrides:

values in class AbstractMapDecorator

Returns:

a collection view of the values contained in this map

containsValue

public boolean containsValue(java.lang.Object key,
                             java.lang.Object value)

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

Parameters:

value - the value to search for

Returns:

true if the map contains the value

getCollection

public java.util.Collection getCollection(java.lang.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(java.lang.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(java.lang.Object key,
                      java.util.Collection 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 java.util.Iterator iterator(java.lang.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

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