Package 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:
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
Version:
$Revision: 1713175 $ $Date: 2015-11-07 21:47:04 +0100 (Sat, 07 Nov 2015) $
Author:
James Carman, Christopher Berry, James Strachan, Steve Downey, Stephen Colebourne, Julien Buret, Serhiy Yevtushenko

  • 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

    • 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).

    • clear

      public void clear()
      Clear the map.
      Specified by:
      clear in interface Map
      Overrides:
      clear in class AbstractMapDecorator

    • removeMapping

      public Object removeMapping(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:
      removeMapping 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(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
      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 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 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(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 Map
      Overrides:
      putAll in class AbstractMapDecorator
      Parameters:
      map - the map to copy (either a normal or multi map)

    • 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 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(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

    • 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

    • 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(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

    • 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

    • 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 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