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

      All Methods Static Methods Concrete Methods 
      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