/
CollectionUtils.java
613 lines (550 loc) · 16.8 KB
/
CollectionUtils.java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
/*
* Copyright 2002-2019 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.io.Serializable;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedList;
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 {
/**
* 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());
}
/**
* Convert the supplied array into a List. A primitive array gets converted
* into a List of the appropriate wrapper type.
* <p><b>NOTE:</b> 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.
* <p>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[])
*/
@SuppressWarnings("rawtypes")
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 <E> void mergeArrayIntoCollection(@Nullable Object array, Collection<E> 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.
* <p>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 <K, V> void mergePropertiesIntoMap(@Nullable Properties props, Map<K, V> 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.
* <p>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) {
if (isEmpty(source) || isEmpty(candidates)) {
return false;
}
for (Object candidate : candidates) {
if (source.contains(candidate)) {
return true;
}
}
return false;
}
/**
* 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> E findFirstMatch(Collection<?> source, Collection<E> 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> T findValueOfType(Collection<?> collection, @Nullable Class<T> 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 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> T lastElement(@Nullable Set<T> set) {
if (isEmpty(set)) {
return null;
}
if (set instanceof SortedSet) {
return ((SortedSet<T>) set).last();
}
// Full iteration necessary...
Iterator<T> 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> T lastElement(@Nullable List<T> list) {
if (isEmpty(list)) {
return null;
}
return list.get(list.size() - 1);
}
/**
* 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
* @see SortedSet
* @see LinkedHashMap#keySet()
* @see java.util.LinkedHashSet
*/
@Nullable
public static <T> T firstElement(@Nullable Set<T> set) {
if (isEmpty(set)) {
return null;
}
if (set instanceof SortedSet) {
return ((SortedSet<T>) set).first();
}
Iterator<T> 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
*/
@Nullable
public static <T> T firstElement(@Nullable List<T> list) {
if (isEmpty(list)) {
return null;
}
return list.get(0);
}
/**
* 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, E extends A> A[] toArray(Enumeration<E> enumeration, A[] array) {
ArrayList<A> 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 <E> Iterator<E> toIterator(@Nullable Enumeration<E> enumeration) {
return (enumeration != null ? new EnumerationIterator<>(enumeration) : Collections.emptyIterator());
}
/**
* Adapt a {@code Map<K, List<V>>} to an {@code MultiValueMap<K, V>}.
* @param map the original map
* @return the multi-value map
* @since 3.1
*/
public static <K, V> MultiValueMap<K, V> toMultiValueMap(Map<K, List<V>> map) {
return new MultiValueMapAdapter<>(map);
}
/**
* Return an unmodifiable view of the specified multi-value map.
* @param map 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 <K, V> MultiValueMap<K, V> unmodifiableMultiValueMap(MultiValueMap<? extends K, ? extends V> map) {
Assert.notNull(map, "'map' must not be null");
Map<K, List<V>> result = new LinkedHashMap<>(map.size());
map.forEach((key, value) -> {
List<? extends V> values = Collections.unmodifiableList(value);
result.put(key, (List<V>) values);
});
Map<K, List<V>> unmodifiableMap = Collections.unmodifiableMap(result);
return toMultiValueMap(unmodifiableMap);
}
/**
* Iterator wrapping an Enumeration.
*/
private static class EnumerationIterator<E> implements Iterator<E> {
private final Enumeration<E> enumeration;
public EnumerationIterator(Enumeration<E> 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");
}
}
/**
* Adapts a Map to the MultiValueMap contract.
*/
@SuppressWarnings("serial")
private static class MultiValueMapAdapter<K, V> implements MultiValueMap<K, V>, Serializable {
private final Map<K, List<V>> map;
public MultiValueMapAdapter(Map<K, List<V>> map) {
Assert.notNull(map, "'map' must not be null");
this.map = map;
}
@Override
@Nullable
public V getFirst(K key) {
List<V> values = this.map.get(key);
return (values != null ? values.get(0) : null);
}
@Override
public void add(K key, @Nullable V value) {
List<V> values = this.map.computeIfAbsent(key, k -> new LinkedList<>());
values.add(value);
}
@Override
public void addAll(K key, List<? extends V> values) {
List<V> currentValues = this.map.computeIfAbsent(key, k -> new LinkedList<>());
currentValues.addAll(values);
}
@Override
public void addAll(MultiValueMap<K, V> values) {
for (Entry<K, List<V>> entry : values.entrySet()) {
addAll(entry.getKey(), entry.getValue());
}
}
@Override
public void set(K key, @Nullable V value) {
List<V> values = new LinkedList<>();
values.add(value);
this.map.put(key, values);
}
@Override
public void setAll(Map<K, V> values) {
values.forEach(this::set);
}
@Override
public Map<K, V> toSingleValueMap() {
LinkedHashMap<K, V> singleValueMap = new LinkedHashMap<>(this.map.size());
this.map.forEach((key, value) -> singleValueMap.put(key, value.get(0)));
return singleValueMap;
}
@Override
public int size() {
return this.map.size();
}
@Override
public boolean isEmpty() {
return this.map.isEmpty();
}
@Override
public boolean containsKey(Object key) {
return this.map.containsKey(key);
}
@Override
public boolean containsValue(Object value) {
return this.map.containsValue(value);
}
@Override
public List<V> get(Object key) {
return this.map.get(key);
}
@Override
public List<V> put(K key, List<V> value) {
return this.map.put(key, value);
}
@Override
public List<V> remove(Object key) {
return this.map.remove(key);
}
@Override
public void putAll(Map<? extends K, ? extends List<V>> map) {
this.map.putAll(map);
}
@Override
public void clear() {
this.map.clear();
}
@Override
public Set<K> keySet() {
return this.map.keySet();
}
@Override
public Collection<List<V>> values() {
return this.map.values();
}
@Override
public Set<Entry<K, List<V>>> entrySet() {
return this.map.entrySet();
}
@Override
public boolean equals(@Nullable Object other) {
if (this == other) {
return true;
}
return this.map.equals(other);
}
@Override
public int hashCode() {
return this.map.hashCode();
}
@Override
public String toString() {
return this.map.toString();
}
}
}