Class CollectionUtils
- Since:
- 1.1.3
- Author:
- Juergen Hoeller, Rob Harrop, Arjen Poutsma
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Constructor Summary
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Method Summary
Modifier and TypeMethodDescriptionstatic List<?>
arrayToList
(Object source) Convert the supplied array into a List.static <K,
V> Map<K, V> compositeMap
(Map<K, V> first, Map<K, V> second) Return a (partially unmodifiable) map that combines the provided two maps.static <K,
V> Map<K, V> compositeMap
(Map<K, V> first, Map<K, V> second, BiFunction<K, V, V> putFunction, Consumer<Map<K, V>> putAllFunction) Return a map that combines the provided maps.static boolean
contains
(Enumeration<?> enumeration, Object element) Check whether the given Enumeration contains the given element.static boolean
Check whether the given Iterator contains the given element.static boolean
containsAny
(Collection<?> source, Collection<?> candidates) Returntrue
if any element in 'candidates
' is contained in 'source
'; otherwise returnsfalse
.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 <E> E
findFirstMatch
(Collection<?> source, Collection<E> 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 <T> T
firstElement
(List<T> list) Retrieve the first element of the given List, accessing the zero index.static <T> T
firstElement
(Set<T> set) Retrieve the first element of the given Set, usingSortedSet.first()
or otherwise using the iterator.static boolean
hasUniqueObject
(Collection<?> collection) Determine whether the given Collection only contains a single unique object.static boolean
isEmpty
(Collection<?> collection) Returntrue
if the supplied Collection isnull
or empty.static boolean
Returntrue
if the supplied Map isnull
or empty.static <T> T
lastElement
(List<T> list) Retrieve the last element of the given List, accessing the highest index.static <T> T
lastElement
(Set<T> set) Retrieve the last element of the given Set, usingSortedSet.last()
or otherwise iterating over all elements (assuming a linked set).static <E> void
mergeArrayIntoCollection
(Object array, Collection<E> collection) Merge the given array into the given Collection.static <K,
V> void mergePropertiesIntoMap
(Properties props, Map<K, V> map) Merge the given Properties instance into the given Map, copying all properties (key-value pairs) over.static <K,
V> HashMap<K, V> newHashMap
(int expectedSize) Instantiate a newHashMap
with an initial capacity that can accommodate the specified number of elements without any immediate resize/rehash operations to be expected.static <E> HashSet<E>
newHashSet
(int expectedSize) Instantiate a newHashSet
with an initial capacity that can accommodate the specified number of elements without any immediate resize/rehash operations to be expected.static <K,
V> LinkedHashMap<K, V> newLinkedHashMap
(int expectedSize) Instantiate a newLinkedHashMap
with an initial capacity that can accommodate the specified number of elements without any immediate resize/rehash operations to be expected.static <E> LinkedHashSet<E>
newLinkedHashSet
(int expectedSize) Instantiate a newLinkedHashSet
with an initial capacity that can accommodate the specified number of elements without any immediate resize/rehash operations to be expected.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 anEnumeration
to anIterator
.static <K,
V> MultiValueMap<K, V> toMultiValueMap
(Map<K, List<V>> targetMap) Adapt aMap<K, List<V>>
to anMultiValueMap<K, V>
.static <K,
V> MultiValueMap<K, V> unmodifiableMultiValueMap
(MultiValueMap<? extends K, ? extends V> targetMap) Return an unmodifiable view of the specified multi-value map.
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Constructor Details
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CollectionUtils
public CollectionUtils()
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Method Details
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isEmpty
Returntrue
if the supplied Collection isnull
or empty. Otherwise, returnfalse
.- Parameters:
collection
- the Collection to check- Returns:
- whether the given Collection is empty
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isEmpty
Returntrue
if the supplied Map isnull
or empty. Otherwise, returnfalse
.- Parameters:
map
- the Map to check- Returns:
- whether the given Map is empty
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newHashMap
Instantiate a newHashMap
with an initial capacity that can accommodate the specified number of elements without any immediate resize/rehash operations to be expected.This differs from the regular
HashMap
constructor which takes an initial capacity relative to a load factor but is effectively aligned with the JDK'sConcurrentHashMap(int)
.- Parameters:
expectedSize
- the expected number of elements (with a corresponding capacity to be derived so that no resize/rehash operations are needed)- Since:
- 5.3
- See Also:
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newLinkedHashMap
Instantiate a newLinkedHashMap
with an initial capacity that can accommodate the specified number of elements without any immediate resize/rehash operations to be expected.This differs from the regular
LinkedHashMap
constructor which takes an initial capacity relative to a load factor but is aligned with Spring's ownLinkedCaseInsensitiveMap
andLinkedMultiValueMap
constructor semantics as of 5.3.- Parameters:
expectedSize
- the expected number of elements (with a corresponding capacity to be derived so that no resize/rehash operations are needed)- Since:
- 5.3
- See Also:
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newHashSet
Instantiate a newHashSet
with an initial capacity that can accommodate the specified number of elements without any immediate resize/rehash operations to be expected.- Parameters:
expectedSize
- the expected number of elements (with a corresponding capacity to be derived so that no resize/rehash operations are needed)- Since:
- 6.2
- See Also:
-
newLinkedHashSet
Instantiate a newLinkedHashSet
with an initial capacity that can accommodate the specified number of elements without any immediate resize/rehash operations to be expected.- Parameters:
expectedSize
- the expected number of elements (with a corresponding capacity to be derived so that no resize/rehash operations are needed)- Since:
- 6.2
- See Also:
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arrayToList
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. ThisarrayToList
method is just meant to deal with an incoming Object value that might be anObject[]
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:
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mergeArrayIntoCollection
Merge the given array into the given Collection.- Parameters:
array
- the array to merge (may benull
)collection
- the target Collection to merge the array into
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mergePropertiesIntoMap
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 benull
)map
- the target Map to merge the properties into
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contains
Check whether the given Iterator contains the given element.- Parameters:
iterator
- the Iterator to checkelement
- the element to look for- Returns:
true
if found,false
otherwise
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contains
Check whether the given Enumeration contains the given element.- Parameters:
enumeration
- the Enumeration to checkelement
- the element to look for- Returns:
true
if found,false
otherwise
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containsInstance
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 checkelement
- the element to look for- Returns:
true
if found,false
otherwise
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containsAny
Returntrue
if any element in 'candidates
' is contained in 'source
'; otherwise returnsfalse
.- Parameters:
source
- the source Collectioncandidates
- the candidates to search for- Returns:
- whether any of the candidates has been found
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findFirstMatch
Return the first element in 'candidates
' that is contained in 'source
'. If no element in 'candidates
' is present in 'source
' returnsnull
. Iteration order isCollection
implementation specific.- Parameters:
source
- the source Collectioncandidates
- the candidates to search for- Returns:
- the first present object, or
null
if not found
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findValueOfType
Find a single value of the given type in the given Collection.- Parameters:
collection
- the Collection to searchtype
- 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
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findValueOfType
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 searchtypes
- 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
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hasUniqueObject
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
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findCommonElementType
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)
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firstElement
Retrieve the first element of the given Set, usingSortedSet.first()
or otherwise using the iterator.- Parameters:
set
- the Set to check (may benull
or empty)- Returns:
- the first element, or
null
if none - Since:
- 5.2.3
- See Also:
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firstElement
Retrieve the first element of the given List, accessing the zero index.- Parameters:
list
- the List to check (may benull
or empty)- Returns:
- the first element, or
null
if none - Since:
- 5.2.3
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lastElement
Retrieve the last element of the given Set, usingSortedSet.last()
or otherwise iterating over all elements (assuming a linked set).- Parameters:
set
- the Set to check (may benull
or empty)- Returns:
- the last element, or
null
if none - Since:
- 5.0.3
- See Also:
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lastElement
Retrieve the last element of the given List, accessing the highest index.- Parameters:
list
- the List to check (may benull
or empty)- Returns:
- the last element, or
null
if none - Since:
- 5.0.3
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toArray
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
Adapt anEnumeration
to anIterator
.- Parameters:
enumeration
- the originalEnumeration
- Returns:
- the adapted
Iterator
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toMultiValueMap
Adapt aMap<K, List<V>>
to anMultiValueMap<K, V>
.- Parameters:
targetMap
- the original map- Returns:
- the adapted multi-value map (wrapping the original map)
- Since:
- 3.1
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unmodifiableMultiValueMap
public static <K,V> MultiValueMap<K,V> unmodifiableMultiValueMap(MultiValueMap<? extends K, ? extends V> targetMap) Return an unmodifiable view of the specified multi-value map.- Parameters:
targetMap
- the map for which an unmodifiable view is to be returned.- Returns:
- an unmodifiable view of the specified multi-value map
- Since:
- 3.1
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compositeMap
Return a (partially unmodifiable) map that combines the provided two maps. InvokingMap.put(Object, Object)
orMap.putAll(Map)
on the returned map results in anUnsupportedOperationException
.In the case of a key collision,
first
takes precedence oversecond
. In other words, entries insecond
with a key that is also mapped byfirst
are effectively ignored.- Parameters:
first
- the first map to composesecond
- the second map to compose- Returns:
- a new map that composes the given two maps
- Since:
- 6.2
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compositeMap
public static <K,V> Map<K,V> compositeMap(Map<K, V> first, Map<K, V> second, @Nullable BiFunction<K, V, V> putFunction, @Nullable Consumer<Map<K, V>> putAllFunction) Return a map that combines the provided maps. InvokingMap.put(Object, Object)
on the returned map will applyputFunction
, or will throw anUnsupportedOperationException
putFunction
isnull
. The same applies toMap.putAll(Map)
andputAllFunction
.In the case of a key collision,
first
takes precedence oversecond
. In other words, entries insecond
with a key that is also mapped byfirst
are effectively ignored.- Parameters:
first
- the first map to composesecond
- the second map to composeputFunction
- applied whenMap::put
is invoked. Ifnull
,Map::put
throws anUnsupportedOperationException
.putAllFunction
- applied whenMap::putAll
is invoked. Ifnull
,Map::putAll
throws anUnsupportedOperationException
.- Returns:
- a new map that composes the give maps
- Since:
- 6.2
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