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## org.springframework.util
Class CollectionUtils

    java.lang.Object
      org.springframework.util.CollectionUtils

    public abstract class CollectionUtils

extends Object

Miscellaneous collection utility methods. Mainly for internal use within the framework.

Since:
  1.1.3
Author:
  Juergen Hoeller, Rob Harrop

Constructor Summary
`CollectionUtils()`

Method Summary
`static List` | `arrayToList(Object source)` Convert the supplied array into a List.
`static boolean` | `contains(Enumeration enumeration, Object element)` Check whether the given Enumeration contains the given element.
`static boolean` | `contains(Iterator iterator, Object element)` Check whether the given Iterator contains the given element.
`static boolean` | `containsAny(Collection source, Collection candidates)` Return `true` if any element in '`candidates`' is contained in '`source`'; otherwise returns `false`.
`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 Object` | `findFirstMatch(Collection source, Collection 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 boolean` | `hasUniqueObject(Collection collection)` Determine whether the given Collection only contains a single unique object.
`static boolean` | `isEmpty(Collection collection)` Return `true` if the supplied Collection is `null` or empty.
`static boolean` | `isEmpty(Map map)` Return `true` if the supplied Map is `null` or empty.
`static void` | `mergeArrayIntoCollection(Object array, Collection collection)` Merge the given array into the given Collection.
`static void` | `mergePropertiesIntoMap(Properties props, Map map)` Merge the given Properties instance into the given Map, copying all properties (key-value pairs) over.
`static
`<E> Iterator<E>`
` | `toIterator(Enumeration<E> enumeration)` Adapts an enumeration to an iterator.

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(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.

  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)`

### mergeArrayIntoCollection

    public static void mergeArrayIntoCollection(Object array,
                                                Collection 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 void mergePropertiesIntoMap(Properties props,
                                              Map 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` else

### 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` else

### 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` else

### 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 Object findFirstMatch(Collection source,
                                        Collection 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` else

### 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)

### toIterator

    public static <E> Iterator<E> toIterator(Enumeration<E> enumeration)

  Adapts an enumeration to an iterator.

  Parameters:
    `enumeration` - the enumeration
  Returns:
    the iterator

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