org.springframework.util

Class CollectionUtils

java.lang.Object

org.springframework.util.CollectionUtils

public abstract class CollectionUtils
extends java.lang.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

Constructors

Constructor and Description
CollectionUtils()

Method Summary

Modifier and Type	Method and Description
static java.util.List	arrayToList(java.lang.Object source) Convert the supplied array into a List.
static boolean	contains(java.util.Enumeration<?> enumeration, java.lang.Object element) Check whether the given Enumeration contains the given element.
static boolean	contains(java.util.Iterator<?> iterator, java.lang.Object element) Check whether the given Iterator contains the given element.
static boolean	containsAny(java.util.Collection<?> source, java.util.Collection<?> candidates) Return true if any element in 'candidates' is contained in 'source'; otherwise returns false.
static boolean	containsInstance(java.util.Collection<?> collection, java.lang.Object element) Check whether the given Collection contains the given element instance.
static java.lang.Class<?>	findCommonElementType(java.util.Collection<?> collection) Find the common element type of the given Collection, if any.
static <E> E	findFirstMatch(java.util.Collection<?> source, java.util.Collection<E> candidates) Return the first element in 'candidates' that is contained in 'source'.
static java.lang.Object	findValueOfType(java.util.Collection<?> collection, java.lang.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(java.util.Collection<?> collection, java.lang.Class<T> type) Find a single value of the given type in the given Collection.
static boolean	hasUniqueObject(java.util.Collection<?> collection) Determine whether the given Collection only contains a single unique object.
static boolean	isEmpty(java.util.Collection<?> collection) Return true if the supplied Collection is null or empty.
static boolean	isEmpty(java.util.Map<?,?> map) Return true if the supplied Map is null or empty.
static <T> T	lastElement(java.util.List<T> list) Retrieve the last element of the given List, accessing the highest index.
static <T> T	lastElement(java.util.Set<T> set) Retrieve the last element of the given Set, using SortedSet.last() or otherwise iterating over all elements (assuming a linked set).
static <E> void	mergeArrayIntoCollection(java.lang.Object array, java.util.Collection<E> collection) Merge the given array into the given Collection.
static <K,V> void	mergePropertiesIntoMap(java.util.Properties props, java.util.Map<K,V> map) Merge the given Properties instance into the given Map, copying all properties (key-value pairs) over.
static <A,E extends A> A[]	toArray(java.util.Enumeration<E> enumeration, A[] array) Marshal the elements from the given enumeration into an array of the given type.
static <E> java.util.Iterator<E>	toIterator(java.util.Enumeration<E> enumeration) Adapt an enumeration to an iterator.
static <K,V> MultiValueMap<K,V>	toMultiValueMap(java.util.Map<K,java.util.List<V>> map) Adapt a Map<K, List<V>> to an MultiValueMap<K, V>.
static <K,V> MultiValueMap<K,V>	unmodifiableMultiValueMap(MultiValueMap<? extends K,? extends V> map) Return 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(@Nullable
                              java.util.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(@Nullable
                              java.util.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 java.util.List arrayToList(@Nullable
                                         java.lang.Object source)

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

NOTE: Generally prefer the standard Arrays.asList(T...) method. This arrayToList method is just meant to deal with an incoming Object value that might be an Object[] or a primitive array at runtime.

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), Arrays.asList(Object[])

mergeArrayIntoCollection

public static <E> void mergeArrayIntoCollection(@Nullable
                                                java.lang.Object array,
                                                java.util.Collection<E> 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 <K,V> void mergePropertiesIntoMap(@Nullable
                                                java.util.Properties props,
                                                java.util.Map<K,V> 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(@Nullable
                               java.util.Iterator<?> iterator,
                               java.lang.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 otherwise

contains

public static boolean contains(@Nullable
                               java.util.Enumeration<?> enumeration,
                               java.lang.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 otherwise

containsInstance

public static boolean containsInstance(@Nullable
                                       java.util.Collection<?> collection,
                                       java.lang.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 otherwise

containsAny

public static boolean containsAny(java.util.Collection<?> source,
                                  java.util.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

@Nullable
public static <E> E findFirstMatch(java.util.Collection<?> source,
                                             java.util.Collection<E> 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

@Nullable
public static <T> T findValueOfType(java.util.Collection<?> collection,
                                              @Nullable
                                              java.lang.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

@Nullable
public static java.lang.Object findValueOfType(java.util.Collection<?> collection,
                                                         java.lang.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(java.util.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 otherwise

findCommonElementType

@Nullable
public static java.lang.Class<?> findCommonElementType(java.util.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)

lastElement

@Nullable
public static <T> T lastElement(@Nullable
                                          java.util.Set<T> set)

Retrieve the last element of the given Set, using SortedSet.last() or otherwise iterating over all elements (assuming a linked set).

Parameters:

set - the Set to check (may be null or empty)

Returns:

the last element, or null if none

Since:

5.0.3

See Also:

SortedSet, LinkedHashMap.keySet(), LinkedHashSet

lastElement

@Nullable
public static <T> T lastElement(@Nullable
                                          java.util.List<T> list)

Retrieve the last element of the given List, accessing the highest index.

Parameters:

list - the List to check (may be null or empty)

Returns:

the last element, or null if none

Since:

5.0.3

toArray

public static <A,E extends A> A[] toArray(java.util.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> java.util.Iterator<E> toIterator(java.util.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(java.util.Map<K,java.util.List<V>> map)

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

Parameters:

map - the original map

Returns:

the multi-value map

Since:

3.1

unmodifiableMultiValueMap

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

Return 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.

Since:

3.1