org.springframework.util.CollectionUtils Maven / Gradle / Ivy
/*
* Copyright 2002-2020 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.util;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.Set;
import java.util.SortedSet;
import org.springframework.lang.Nullable;
/**
* Miscellaneous collection utility methods.
* Mainly for internal use within the framework.
*
* @author Juergen Hoeller
* @author Rob Harrop
* @author Arjen Poutsma
* @since 1.1.3
*/
public abstract class CollectionUtils {
/**
* Default load factor for {@link HashMap}/{@link LinkedHashMap} variants.
* @see #newHashMap(int)
* @see #newLinkedHashMap(int)
*/
static final float DEFAULT_LOAD_FACTOR = 0.75f;
/**
* Return {@code true} if the supplied Collection is {@code null} or empty.
* Otherwise, return {@code false}.
* @param collection the Collection to check
* @return whether the given Collection is empty
*/
public static boolean isEmpty(@Nullable Collection collection) {
return (collection == null || collection.isEmpty());
}
/**
* Return {@code true} if the supplied Map is {@code null} or empty.
* Otherwise, return {@code false}.
* @param map the Map to check
* @return whether the given Map is empty
*/
public static boolean isEmpty(@Nullable Map map) {
return (map == null || map.isEmpty());
}
/**
* Instantiate a new {@link HashMap} with an initial capacity
* that can accommodate the specified number of elements without
* any immediate resize/rehash operations to be expected.
* This differs from the regular {@link HashMap} constructor
* which takes an initial capacity relative to a load factor
* but is effectively aligned with the JDK's
* {@link java.util.concurrent.ConcurrentHashMap#ConcurrentHashMap(int)}.
* @param expectedSize the expected number of elements (with a corresponding
* capacity to be derived so that no resize/rehash operations are needed)
* @since 5.3
* @see #newLinkedHashMap(int)
*/
public static HashMap newHashMap(int expectedSize) {
return new HashMap<>((int) (expectedSize / DEFAULT_LOAD_FACTOR), DEFAULT_LOAD_FACTOR);
}
/**
* Instantiate a new {@link LinkedHashMap} with an initial capacity
* that can accommodate the specified number of elements without
* any immediate resize/rehash operations to be expected.
* This differs from the regular {@link LinkedHashMap} constructor
* which takes an initial capacity relative to a load factor but is
* aligned with Spring's own {@link LinkedCaseInsensitiveMap} and
* {@link LinkedMultiValueMap} constructor semantics as of 5.3.
* @param expectedSize the expected number of elements (with a corresponding
* capacity to be derived so that no resize/rehash operations are needed)
* @since 5.3
* @see #newHashMap(int)
*/
public static LinkedHashMap newLinkedHashMap(int expectedSize) {
return new LinkedHashMap<>((int) (expectedSize / DEFAULT_LOAD_FACTOR), DEFAULT_LOAD_FACTOR);
}
/**
* 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 {@link Arrays#asList} method.
* This {@code arrayToList} method is just meant to deal with an incoming Object
* value that might be an {@code Object[]} or a primitive array at runtime.
*
A {@code null} source value will be converted to an empty List.
* @param source the (potentially primitive) array
* @return the converted List result
* @see ObjectUtils#toObjectArray(Object)
* @see Arrays#asList(Object[])
*/
public static List arrayToList(@Nullable Object source) {
return Arrays.asList(ObjectUtils.toObjectArray(source));
}
/**
* Merge the given array into the given Collection.
* @param array the array to merge (may be {@code null})
* @param collection the target Collection to merge the array into
*/
@SuppressWarnings("unchecked")
public static void mergeArrayIntoCollection(@Nullable Object array, Collection collection) {
Object[] arr = ObjectUtils.toObjectArray(array);
for (Object elem : arr) {
collection.add((E) elem);
}
}
/**
* Merge the given Properties instance into the given Map,
* copying all properties (key-value pairs) over.
* Uses {@code Properties.propertyNames()} to even catch
* default properties linked into the original Properties instance.
* @param props the Properties instance to merge (may be {@code null})
* @param map the target Map to merge the properties into
*/
@SuppressWarnings("unchecked")
public static void mergePropertiesIntoMap(@Nullable Properties props, Map map) {
if (props != null) {
for (Enumeration en = props.propertyNames(); en.hasMoreElements();) {
String key = (String) en.nextElement();
Object value = props.get(key);
if (value == null) {
// Allow for defaults fallback or potentially overridden accessor...
value = props.getProperty(key);
}
map.put((K) key, (V) value);
}
}
}
/**
* Check whether the given Iterator contains the given element.
* @param iterator the Iterator to check
* @param element the element to look for
* @return {@code true} if found, {@code false} otherwise
*/
public static boolean contains(@Nullable Iterator iterator, Object element) {
if (iterator != null) {
while (iterator.hasNext()) {
Object candidate = iterator.next();
if (ObjectUtils.nullSafeEquals(candidate, element)) {
return true;
}
}
}
return false;
}
/**
* Check whether the given Enumeration contains the given element.
* @param enumeration the Enumeration to check
* @param element the element to look for
* @return {@code true} if found, {@code false} otherwise
*/
public static boolean contains(@Nullable Enumeration enumeration, Object element) {
if (enumeration != null) {
while (enumeration.hasMoreElements()) {
Object candidate = enumeration.nextElement();
if (ObjectUtils.nullSafeEquals(candidate, element)) {
return true;
}
}
}
return false;
}
/**
* Check whether the given Collection contains the given element instance.
* Enforces the given instance to be present, rather than returning
* {@code true} for an equal element as well.
* @param collection the Collection to check
* @param element the element to look for
* @return {@code true} if found, {@code false} otherwise
*/
public static boolean containsInstance(@Nullable Collection collection, Object element) {
if (collection != null) {
for (Object candidate : collection) {
if (candidate == element) {
return true;
}
}
}
return false;
}
/**
* Return {@code true} if any element in '{@code candidates}' is
* contained in '{@code source}'; otherwise returns {@code false}.
* @param source the source Collection
* @param candidates the candidates to search for
* @return whether any of the candidates has been found
*/
public static boolean containsAny(Collection source, Collection candidates) {
return findFirstMatch(source, candidates) != null;
}
/**
* Return the first element in '{@code candidates}' that is contained in
* '{@code source}'. If no element in '{@code candidates}' is present in
* '{@code source}' returns {@code null}. Iteration order is
* {@link Collection} implementation specific.
* @param source the source Collection
* @param candidates the candidates to search for
* @return the first present object, or {@code null} if not found
*/
@SuppressWarnings("unchecked")
@Nullable
public static E findFirstMatch(Collection source, Collection candidates) {
if (isEmpty(source) || isEmpty(candidates)) {
return null;
}
for (Object candidate : candidates) {
if (source.contains(candidate)) {
return (E) candidate;
}
}
return null;
}
/**
* Find a single value of the given type in the given Collection.
* @param collection the Collection to search
* @param type the type to look for
* @return a value of the given type found if there is a clear match,
* or {@code null} if none or more than one such value found
*/
@SuppressWarnings("unchecked")
@Nullable
public static T findValueOfType(Collection collection, @Nullable Class type) {
if (isEmpty(collection)) {
return null;
}
T value = null;
for (Object element : collection) {
if (type == null || type.isInstance(element)) {
if (value != null) {
// More than one value found... no clear single value.
return null;
}
value = (T) element;
}
}
return value;
}
/**
* 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.
* @param collection the collection to search
* @param types the types to look for, in prioritized order
* @return a value of one of the given types found if there is a clear match,
* or {@code null} if none or more than one such value found
*/
@Nullable
public static Object findValueOfType(Collection collection, Class[] types) {
if (isEmpty(collection) || ObjectUtils.isEmpty(types)) {
return null;
}
for (Class type : types) {
Object value = findValueOfType(collection, type);
if (value != null) {
return value;
}
}
return null;
}
/**
* Determine whether the given Collection only contains a single unique object.
* @param collection the Collection to check
* @return {@code true} if the collection contains a single reference or
* multiple references to the same instance, {@code false} otherwise
*/
public static boolean hasUniqueObject(Collection collection) {
if (isEmpty(collection)) {
return false;
}
boolean hasCandidate = false;
Object candidate = null;
for (Object elem : collection) {
if (!hasCandidate) {
hasCandidate = true;
candidate = elem;
}
else if (candidate != elem) {
return false;
}
}
return true;
}
/**
* Find the common element type of the given Collection, if any.
* @param collection the Collection to check
* @return the common element type, or {@code null} if no clear
* common type has been found (or the collection was empty)
*/
@Nullable
public static Class findCommonElementType(Collection collection) {
if (isEmpty(collection)) {
return null;
}
Class candidate = null;
for (Object val : collection) {
if (val != null) {
if (candidate == null) {
candidate = val.getClass();
}
else if (candidate != val.getClass()) {
return null;
}
}
}
return candidate;
}
/**
* Retrieve the first element of the given Set, using {@link SortedSet#first()}
* or otherwise using the iterator.
* @param set the Set to check (may be {@code null} or empty)
* @return the first element, or {@code null} if none
* @since 5.2.3
* @see SortedSet
* @see LinkedHashMap#keySet()
* @see java.util.LinkedHashSet
*/
@Nullable
public static T firstElement(@Nullable Set set) {
if (isEmpty(set)) {
return null;
}
if (set instanceof SortedSet) {
return ((SortedSet) set).first();
}
Iterator it = set.iterator();
T first = null;
if (it.hasNext()) {
first = it.next();
}
return first;
}
/**
* Retrieve the first element of the given List, accessing the zero index.
* @param list the List to check (may be {@code null} or empty)
* @return the first element, or {@code null} if none
* @since 5.2.3
*/
@Nullable
public static T firstElement(@Nullable List list) {
if (isEmpty(list)) {
return null;
}
return list.get(0);
}
/**
* Retrieve the last element of the given Set, using {@link SortedSet#last()}
* or otherwise iterating over all elements (assuming a linked set).
* @param set the Set to check (may be {@code null} or empty)
* @return the last element, or {@code null} if none
* @since 5.0.3
* @see SortedSet
* @see LinkedHashMap#keySet()
* @see java.util.LinkedHashSet
*/
@Nullable
public static T lastElement(@Nullable Set set) {
if (isEmpty(set)) {
return null;
}
if (set instanceof SortedSet) {
return ((SortedSet) set).last();
}
// Full iteration necessary...
Iterator it = set.iterator();
T last = null;
while (it.hasNext()) {
last = it.next();
}
return last;
}
/**
* Retrieve the last element of the given List, accessing the highest index.
* @param list the List to check (may be {@code null} or empty)
* @return the last element, or {@code null} if none
* @since 5.0.3
*/
@Nullable
public static T lastElement(@Nullable List list) {
if (isEmpty(list)) {
return null;
}
return list.get(list.size() - 1);
}
/**
* 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.
*/
public static A[] toArray(Enumeration enumeration, A[] array) {
ArrayList elements = new ArrayList<>();
while (enumeration.hasMoreElements()) {
elements.add(enumeration.nextElement());
}
return elements.toArray(array);
}
/**
* Adapt an {@link Enumeration} to an {@link Iterator}.
* @param enumeration the original {@code Enumeration}
* @return the adapted {@code Iterator}
*/
public static Iterator toIterator(@Nullable Enumeration enumeration) {
return (enumeration != null ? new EnumerationIterator<>(enumeration) : Collections.emptyIterator());
}
/**
* Adapt a {@code Map>} to an {@code MultiValueMap}.
* @param targetMap the original map
* @return the adapted multi-value map (wrapping the original map)
* @since 3.1
*/
public static MultiValueMap toMultiValueMap(Map> targetMap) {
return new MultiValueMapAdapter<>(targetMap);
}
/**
* Return an unmodifiable view of the specified multi-value map.
* @param targetMap the map for which an unmodifiable view is to be returned.
* @return an unmodifiable view of the specified multi-value map
* @since 3.1
*/
@SuppressWarnings("unchecked")
public static MultiValueMap unmodifiableMultiValueMap(
MultiValueMap targetMap) {
Assert.notNull(targetMap, "'targetMap' must not be null");
Map> result = newLinkedHashMap(targetMap.size());
targetMap.forEach((key, value) -> {
List values = Collections.unmodifiableList(value);
result.put(key, (List) values);
});
Map> unmodifiableMap = Collections.unmodifiableMap(result);
return toMultiValueMap(unmodifiableMap);
}
/**
* Iterator wrapping an Enumeration.
*/
private static class EnumerationIterator implements Iterator {
private final Enumeration enumeration;
public EnumerationIterator(Enumeration enumeration) {
this.enumeration = enumeration;
}
@Override
public boolean hasNext() {
return this.enumeration.hasMoreElements();
}
@Override
public E next() {
return this.enumeration.nextElement();
}
@Override
public void remove() throws UnsupportedOperationException {
throw new UnsupportedOperationException("Not supported");
}
}
}