org.apache.commons.collections.map

Class MultiValueMap

Implemented Interfaces:
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.

Version:
$Revision: 348007 $ $Date: 2005-11-21 22:52:57 +0000 (Mon, 21 Nov 2005) $
Authors:
James Carman
Christopher Berry
James Strachan
Steve Downey
Stephen Colebourne
Julien Buret
Serhiy Yevtushenko
Since:
Commons Collections 3.2

Field Summary

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

map

Constructor Summary

MultiValueMap()
Creates a MultiValueMap based on a HashMap and storing the multiple values in an ArrayList.
MultiValueMap(Map map, Factory collectionFactory)
Creates a MultiValueMap which decorates the given map and creates the value collections using the supplied collectionFactory.

Method Summary

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

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

clear, containsKey, containsValue, entrySet, equals, get, getMap, hashCode, isEmpty, keySet, put, putAll, remove, size, toString, values

Constructor Details

MultiValueMap

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

MultiValueMap

protected MultiValueMap(Map map,
                        Factory collectionFactory)
Creates a MultiValueMap which decorates the given map and creates the value collections using the supplied collectionFactory.
Parameters:
map - the map to decorate
collectionFactory - the collection factory which must return a Collection instance

Method Details

clear

public void clear()
Clear the map.
Overrides:
clear in interface AbstractMapDecorator

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 MultiMap
Overrides:
containsValue in interface AbstractMapDecorator
Parameters:
value - the value to search for
Returns:
true if the map contains the value

containsValue

public boolean containsValue(Object key,
                             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

createCollection

protected Collection 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

decorate

public static MultiValueMap decorate(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(Map map,
                                     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(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).

getCollection

public Collection 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

iterator

public Iterator 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

put

public Object put(Object 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 MultiMap
Overrides:
put in interface 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(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).

Overrides:
putAll in interface AbstractMapDecorator
Parameters:
map - the map to copy (either a normal or multi map)

putAll

public boolean putAll(Object key,
                      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

remove

public Object 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 subsequant get(key).

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

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

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

values

public 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 MultiMap
Overrides:
values in interface AbstractMapDecorator
Returns:
a collection view of the values contained in this map

Copyright © 2001-2015 Apache Software Foundation. All Rights Reserved.