CollectionUtils (Spring Framework 3.2.18.RELEASE API)

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, Arjen Poutsma

Constructor Summary

Constructors
Constructor and Description

CollectionUtils()

Constructors
Constructor and Description
`CollectionUtils()`

Method Summary

Methods
Modifier and Type	Method and Description
`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 <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 an enumeration to an iterator.
`static <K,V> MultiValueMap<K,V>`	`toMultiValueMap(Map<K,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(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 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)
  - 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 enumeration
    
    Returns:
    the 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

Class CollectionUtils

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

CollectionUtils

Method Detail

isEmpty

isEmpty

arrayToList

mergeArrayIntoCollection

mergePropertiesIntoMap

contains

contains

containsInstance

containsAny

findFirstMatch

findValueOfType

findValueOfType

hasUniqueObject

findCommonElementType

toArray

toIterator

toMultiValueMap

unmodifiableMultiValueMap