类 CollectionUtils

构造器详细资料

• CollectionUtils

  public CollectionUtils()

方法详细资料

• isEmpty

  public static boolean isEmpty​(@Nullable
                                Collection<?> collection)

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

  参数:

  collection - the Collection to check

  返回:

  whether the given Collection is empty

• isEmpty

  public static boolean isEmpty​(@Nullable
                                Map<?,​?> map)

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

  参数:

  map - the Map to check

  返回:

  whether the given Map is empty

• arrayToList

  public static List arrayToList​(@Nullable
                                 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.

  参数:

  source - the (potentially primitive) array

  返回:

  the converted List result

  另请参阅:

  ObjectUtils.toObjectArray(Object), Arrays.asList(Object[])

• mergeArrayIntoCollection

  public static <E> void mergeArrayIntoCollection​(@Nullable
                                                  Object array,
                                                  Collection<E> collection)

  Merge the given array into the given Collection.

  参数:

  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
                                                        Properties props,
                                                        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.

  参数:

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

  map - the target Map to merge the properties into

• contains

  public static boolean contains​(@Nullable
                                 Iterator<?> iterator,
                                 Object element)

  Check whether the given Iterator contains the given element.

  参数:

  iterator - the Iterator to check

  element - the element to look for

  返回:

  true if found, false otherwise

• contains

  public static boolean contains​(@Nullable
                                 Enumeration<?> enumeration,
                                 Object element)

  Check whether the given Enumeration contains the given element.

  参数:

  enumeration - the Enumeration to check

  element - the element to look for

  返回:

  true if found, false otherwise

• containsInstance

  public static boolean containsInstance​(@Nullable
                                         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.

  参数:

  collection - the Collection to check

  element - the element to look for

  返回:

  true if found, false otherwise

• containsAny

  public static boolean containsAny​(Collection<?> source,
                                    Collection<?> candidates)

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

  参数:

  source - the source Collection

  candidates - the candidates to search for

  返回:

  whether any of the candidates has been found

• findFirstMatch

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

  参数:

  source - the source Collection

  candidates - the candidates to search for

  返回:

  the first present object, or null if not found

• findValueOfType

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

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

  参数:

  collection - the Collection to search

  type - the type to look for

  返回:

  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 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.

  参数:

  collection - the collection to search

  types - the types to look for, in prioritized order

  返回:

  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.

  参数:

  collection - the Collection to check

  返回:

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

• findCommonElementType

  @Nullable
  public static Class<?> findCommonElementType​(Collection<?> collection)

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

  参数:

  collection - the Collection to check

  返回:

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

• firstElement

  @Nullable
  public static <T> T firstElement​(@Nullable
                                   Set<T> set)

  Retrieve the first element of the given Set, using SortedSet.first() or otherwise using the iterator.

  参数:

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

  返回:

  the first element, or null if none

  从以下版本开始:

  5.2.3

  另请参阅:

  SortedSet, LinkedHashMap.keySet(), LinkedHashSet

• firstElement

  @Nullable
  public static <T> T firstElement​(@Nullable
                                   List<T> list)

  Retrieve the first element of the given List, accessing the zero index.

  参数:

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

  返回:

  the first element, or null if none

  从以下版本开始:

  5.2.3

• lastElement

  @Nullable
  public static <T> T lastElement​(@Nullable
                                  Set<T> set)

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

  参数:

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

  返回:

  the last element, or null if none

  从以下版本开始:

  5.0.3

  另请参阅:

  SortedSet, LinkedHashMap.keySet(), LinkedHashSet

• lastElement

  @Nullable
  public static <T> T lastElement​(@Nullable
                                  List<T> list)

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

  参数:

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

  返回:

  the last element, or null if none

  从以下版本开始:

  5.0.3

• 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​(@Nullable
                                           Enumeration<E> enumeration)

  Adapt an Enumeration to an Iterator.

  参数:

  enumeration - the original Enumeration

  返回:

  the adapted Iterator

• toMultiValueMap

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

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

  参数:

  targetMap - the original map

  返回:

  the adapted multi-value map (wrapping the original map)

  从以下版本开始:

  3.1

• 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.

  参数:

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

  返回:

  an unmodifiable view of the specified multi-value map

  从以下版本开始:

  3.1