Class CollectionUtils

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.

  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​(Object array,
                                                  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​(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.

  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 otherwise

• 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 otherwise

• 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 otherwise

• 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 <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.

  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 otherwise

• 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 original Enumeration

  Returns:

  the adapted Iterator

• toMultiValueMap

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