org.springframework.util
Class CollectionUtils

java.lang.Object
  org.springframework.util.CollectionUtils

public abstract class CollectionUtils
extends Object

Miscellaneous collection utility methods. Mainly for internal use within the framework.

Since:

1.1.3

Author:

Juergen Hoeller, Rob Harrop, Arjen Poutsma

Constructor Summary

CollectionUtils()

Method Summary

static List	arrayToList(Object source) Convert the supplied array into a List.
static boolean	contains(Enumeration enumeration, Object element) Check whether the given Enumeration contains the given element.
static boolean	contains(Iterator iterator, Object element) Check whether the given Iterator contains the given element.
static boolean	containsAny(Collection source, Collection candidates) Return true if any element in 'candidates' is contained in 'source'; otherwise returns false.
static boolean	containsInstance(Collection collection, Object element) Check whether the given Collection contains the given element instance.
static Class<?>	findCommonElementType(Collection collection) Find the common element type of the given Collection, if any.
static Object	findFirstMatch(Collection source, Collection candidates) Return the first element in 'candidates' that is contained in 'source'.
static Object	findValueOfType(Collection<?> collection, Class<?>[] types) Find a single value of one of the given types in the given Collection: searching the Collection for a value of the first type, then searching for a value of the second type, etc.
static <T> T	findValueOfType(Collection<?> collection, Class<T> type) Find a single value of the given type in the given Collection.
static boolean	hasUniqueObject(Collection collection) Determine whether the given Collection only contains a single unique object.
static boolean	isEmpty(Collection collection) Return true if the supplied Collection is null or empty.
static boolean	isEmpty(Map map) Return true if the supplied Map is null or empty.
static void	mergeArrayIntoCollection(Object array, Collection collection) Merge the given array into the given Collection.
static void	mergePropertiesIntoMap(Properties props, Map map) Merge the given Properties instance into the given Map, copying all properties (key-value pairs) over.
static <A,E extends A> A[]	toArray(Enumeration<E> enumeration, A[] array) Marshal the elements from the given enumeration into an array of the given type.
static <E> Iterator<E>	toIterator(Enumeration<E> enumeration) Adapt an enumeration to an iterator.
static <K,V> MultiValueMap<K,V>	toMultiValueMap(Map<K,List<V>> map) Adapts a Map<K, List<V>> to an MultiValueMap<K,V>.
static <K,V> MultiValueMap<K,V>	unmodifiableMultiValueMap(MultiValueMap<? extends K,? extends V> map) Returns an unmodifiable view of the specified multi-value map.

Methods inherited from class java.lang.Object

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

Constructor Detail

CollectionUtils

public CollectionUtils()

Method Detail

isEmpty

public static boolean isEmpty(Collection collection)

Return true if the supplied Collection is null or empty. Otherwise, return false.

Parameters:

collection - the Collection to check

Returns:

whether the given Collection is empty

isEmpty

public static boolean isEmpty(Map map)

Return true if the supplied Map is null or empty. Otherwise, return false.

Parameters:

map - the Map to check

Returns:

whether the given Map is empty

arrayToList

public static List arrayToList(Object source)

Convert the supplied array into a List. A primitive array gets converted into a List of the appropriate wrapper type.

A null source value will be converted to an empty List.

Parameters:

source - the (potentially primitive) array

Returns:

the converted List result

See Also:

ObjectUtils.toObjectArray(Object)

mergeArrayIntoCollection

public static void mergeArrayIntoCollection(Object array,
                                            Collection collection)

Merge the given array into the given Collection.

Parameters:

array - the array to merge (may be null)

collection - the target Collection to merge the array into

mergePropertiesIntoMap

public static void mergePropertiesIntoMap(Properties props,
                                          Map map)

Merge the given Properties instance into the given Map, copying all properties (key-value pairs) over.

Uses Properties.propertyNames() to even catch default properties linked into the original Properties instance.

Parameters:

props - the Properties instance to merge (may be null)

map - the target Map to merge the properties into

contains

public static boolean contains(Iterator iterator,
                               Object element)

Check whether the given Iterator contains the given element.

Parameters:

iterator - the Iterator to check

element - the element to look for

Returns:

true if found, false else

contains

public static boolean contains(Enumeration enumeration,
                               Object element)

Check whether the given Enumeration contains the given element.

Parameters:

enumeration - the Enumeration to check

element - the element to look for

Returns:

true if found, false else

containsInstance

public static boolean containsInstance(Collection collection,
                                       Object element)

Check whether the given Collection contains the given element instance.

Enforces the given instance to be present, rather than returning true for an equal element as well.

Parameters:

collection - the Collection to check

element - the element to look for

Returns:

true if found, false else

containsAny

public static boolean containsAny(Collection source,
                                  Collection candidates)

Return true if any element in 'candidates' is contained in 'source'; otherwise returns false.

Parameters:

source - the source Collection

candidates - the candidates to search for

Returns:

whether any of the candidates has been found

findFirstMatch

public static Object findFirstMatch(Collection source,
                                    Collection candidates)

Return the first element in 'candidates' that is contained in 'source'. If no element in 'candidates' is present in 'source' returns null. Iteration order is Collection implementation specific.

Parameters:

source - the source Collection

candidates - the candidates to search for

Returns:

the first present object, or null if not found

findValueOfType

public static <T> T findValueOfType(Collection<?> collection,
                                    Class<T> type)

Find a single value of the given type in the given Collection.

Parameters:

collection - the Collection to search

type - the type to look for

Returns:

a value of the given type found if there is a clear match, or null if none or more than one such value found

findValueOfType

public static Object findValueOfType(Collection<?> collection,
                                     Class<?>[] types)

Find a single value of one of the given types in the given Collection: searching the Collection for a value of the first type, then searching for a value of the second type, etc.

Parameters:

collection - the collection to search

types - the types to look for, in prioritized order

Returns:

a value of one of the given types found if there is a clear match, or null if none or more than one such value found

hasUniqueObject

public static boolean hasUniqueObject(Collection collection)

Determine whether the given Collection only contains a single unique object.

Parameters:

collection - the Collection to check

Returns:

true if the collection contains a single reference or multiple references to the same instance, false else

findCommonElementType

public static Class<?> findCommonElementType(Collection collection)

Find the common element type of the given Collection, if any.

Parameters:

collection - the Collection to check

Returns:

the common element type, or null if no clear common type has been found (or the collection was empty)

toArray

public static <A,E extends A> A[] toArray(Enumeration<E> enumeration,
                                          A[] array)

Marshal the elements from the given enumeration into an array of the given type. Enumeration elements must be assignable to the type of the given array. The array returned will be a different instance than the array given.

toIterator

public static <E> Iterator<E> toIterator(Enumeration<E> enumeration)

Adapt an enumeration to an iterator.

Parameters:

enumeration - the enumeration

Returns:

the iterator

toMultiValueMap

public static <K,V> MultiValueMap<K,V> toMultiValueMap(Map<K,List<V>> map)

Adapts a Map<K, List<V>> to an MultiValueMap<K,V>.

Parameters:

map - the map

Returns:

the multi-value map

unmodifiableMultiValueMap

public static <K,V> MultiValueMap<K,V> unmodifiableMultiValueMap(MultiValueMap<? extends K,? extends V> map)

Returns an unmodifiable view of the specified multi-value map.

Parameters:

map - the map for which an unmodifiable view is to be returned.

Returns:

an unmodifiable view of the specified multi-value map.