001: /*
002: * Copyright 2002-2007 the original author or authors.
003: *
004: * Licensed under the Apache License, Version 2.0 (the "License");
005: * you may not use this file except in compliance with the License.
006: * You may obtain a copy of the License at
007: *
008: * http://www.apache.org/licenses/LICENSE-2.0
009: *
010: * Unless required by applicable law or agreed to in writing, software
011: * distributed under the License is distributed on an "AS IS" BASIS,
012: * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013: * See the License for the specific language governing permissions and
014: * limitations under the License.
015: */
016:
017: package org.springframework.util;
018:
019: import java.util.Arrays;
020: import java.util.Collection;
021: import java.util.Enumeration;
022: import java.util.Iterator;
023: import java.util.List;
024: import java.util.Map;
025: import java.util.Properties;
026:
027: /**
028: * Miscellaneous collection utility methods.
029: * Mainly for internal use within the framework.
030: *
031: * @author Juergen Hoeller
032: * @author Rob Harrop
033: * @since 1.1.3
034: */
035: public abstract class CollectionUtils {
036:
037: /**
038: * Return <code>true</code> if the supplied Collection is <code>null</code>
039: * or empty. Otherwise, return <code>false</code>.
040: * @param collection the Collection to check
041: * @return whether the given Collection is empty
042: */
043: public static boolean isEmpty(Collection collection) {
044: return (collection == null || collection.isEmpty());
045: }
046:
047: /**
048: * Return <code>true</code> if the supplied Map is <code>null</code>
049: * or empty. Otherwise, return <code>false</code>.
050: * @param map the Map to check
051: * @return whether the given Map is empty
052: */
053: public static boolean isEmpty(Map map) {
054: return (map == null || map.isEmpty());
055: }
056:
057: /**
058: * Convert the supplied array into a List. A primitive array gets
059: * converted into a List of the appropriate wrapper type.
060: * <p>A <code>null</code> source value will be converted to an
061: * empty List.
062: * @param source the (potentially primitive) array
063: * @return the converted List result
064: * @see ObjectUtils#toObjectArray(Object)
065: */
066: public static List arrayToList(Object source) {
067: return Arrays.asList(ObjectUtils.toObjectArray(source));
068: }
069:
070: /**
071: * Merge the given array into the given Collection.
072: * @param array the array to merge (may be <code>null</code>)
073: * @param collection the target Collection to merge the array into
074: */
075: public static void mergeArrayIntoCollection(Object array,
076: Collection collection) {
077: if (collection == null) {
078: throw new IllegalArgumentException(
079: "Collection must not be null");
080: }
081: Object[] arr = ObjectUtils.toObjectArray(array);
082: for (int i = 0; i < arr.length; i++) {
083: collection.add(arr[i]);
084: }
085: }
086:
087: /**
088: * Merge the given Properties instance into the given Map,
089: * copying all properties (key-value pairs) over.
090: * <p>Uses <code>Properties.propertyNames()</code> to even catch
091: * default properties linked into the original Properties instance.
092: * @param props the Properties instance to merge (may be <code>null</code>)
093: * @param map the target Map to merge the properties into
094: */
095: public static void mergePropertiesIntoMap(Properties props, Map map) {
096: if (map == null) {
097: throw new IllegalArgumentException("Map must not be null");
098: }
099: if (props != null) {
100: for (Enumeration en = props.propertyNames(); en
101: .hasMoreElements();) {
102: String key = (String) en.nextElement();
103: map.put(key, props.getProperty(key));
104: }
105: }
106: }
107:
108: /**
109: * Check whether the given Iterator contains the given element.
110: * @param iterator the Iterator to check
111: * @param element the element to look for
112: * @return <code>true</code> if found, <code>false</code> else
113: */
114: public static boolean contains(Iterator iterator, Object element) {
115: if (iterator != null) {
116: while (iterator.hasNext()) {
117: Object candidate = iterator.next();
118: if (ObjectUtils.nullSafeEquals(candidate, element)) {
119: return true;
120: }
121: }
122: }
123: return false;
124: }
125:
126: /**
127: * Check whether the given Enumeration contains the given element.
128: * @param enumeration the Enumeration to check
129: * @param element the element to look for
130: * @return <code>true</code> if found, <code>false</code> else
131: */
132: public static boolean contains(Enumeration enumeration,
133: Object element) {
134: if (enumeration != null) {
135: while (enumeration.hasMoreElements()) {
136: Object candidate = enumeration.nextElement();
137: if (ObjectUtils.nullSafeEquals(candidate, element)) {
138: return true;
139: }
140: }
141: }
142: return false;
143: }
144:
145: /**
146: * Check whether the given Collection contains the given element instance.
147: * <p>Enforces the given instance to be present, rather than returning
148: * <code>true</code> for an equal element as well.
149: * @param collection the Collection to check
150: * @param element the element to look for
151: * @return <code>true</code> if found, <code>false</code> else
152: */
153: public static boolean containsInstance(Collection collection,
154: Object element) {
155: if (collection != null) {
156: for (Iterator it = collection.iterator(); it.hasNext();) {
157: Object candidate = it.next();
158: if (candidate == element) {
159: return true;
160: }
161: }
162: }
163: return false;
164: }
165:
166: /**
167: * Return <code>true</code> if any element in '<code>candidates</code>' is
168: * contained in '<code>source</code>'; otherwise returns <code>false</code>.
169: * @param source the source Collection
170: * @param candidates the candidates to search for
171: * @return whether any of the candidates has been found
172: */
173: public static boolean containsAny(Collection source,
174: Collection candidates) {
175: if (isEmpty(source) || isEmpty(candidates)) {
176: return false;
177: }
178: for (Iterator it = candidates.iterator(); it.hasNext();) {
179: if (source.contains(it.next())) {
180: return true;
181: }
182: }
183: return false;
184: }
185:
186: /**
187: * Return the first element in '<code>candidates</code>' that is contained in
188: * '<code>source</code>'. If no element in '<code>candidates</code>' is present in
189: * '<code>source</code>' returns <code>null</code>. Iteration order is
190: * {@link Collection} implementation specific.
191: * @param source the source Collection
192: * @param candidates the candidates to search for
193: * @return the first present object, or <code>null</code> if not found
194: */
195: public static Object findFirstMatch(Collection source,
196: Collection candidates) {
197: if (isEmpty(source) || isEmpty(candidates)) {
198: return null;
199: }
200: for (Iterator it = candidates.iterator(); it.hasNext();) {
201: Object candidate = it.next();
202: if (source.contains(candidate)) {
203: return candidate;
204: }
205: }
206: return null;
207: }
208:
209: /**
210: * Find a value of the given type in the given Collection.
211: * @param collection the Collection to search
212: * @param type the type to look for
213: * @return a value of the given type found, or <code>null</code> if none
214: * @throws IllegalArgumentException if more than one value of the given type found
215: */
216: public static Object findValueOfType(Collection collection,
217: Class type) throws IllegalArgumentException {
218: if (isEmpty(collection)) {
219: return null;
220: }
221: Class typeToUse = (type != null ? type : Object.class);
222: Object value = null;
223: for (Iterator it = collection.iterator(); it.hasNext();) {
224: Object obj = it.next();
225: if (typeToUse.isInstance(obj)) {
226: if (value != null) {
227: throw new IllegalArgumentException(
228: "More than one value of type ["
229: + typeToUse.getName() + "] found");
230: }
231: value = obj;
232: }
233: }
234: return value;
235: }
236:
237: /**
238: * Find a value of one of the given types in the given Collection:
239: * searching the Collection for a value of the first type, then
240: * searching for a value of the second type, etc.
241: * @param collection the collection to search
242: * @param types the types to look for, in prioritized order
243: * @return a of one of the given types found, or <code>null</code> if none
244: * @throws IllegalArgumentException if more than one value of the given type found
245: */
246: public static Object findValueOfType(Collection collection,
247: Class[] types) throws IllegalArgumentException {
248: if (isEmpty(collection) || ObjectUtils.isEmpty(types)) {
249: return null;
250: }
251: for (int i = 0; i < types.length; i++) {
252: Object value = findValueOfType(collection, types[i]);
253: if (value != null) {
254: return value;
255: }
256: }
257: return null;
258: }
259:
260: /**
261: * Determine whether the given Collection only contains a single unique object.
262: * @param collection the Collection to check
263: * @return <code>true</code> if the collection contains a single reference or
264: * multiple references to the same instance, <code>false</code> else
265: */
266: public static boolean hasUniqueObject(Collection collection) {
267: if (isEmpty(collection)) {
268: return false;
269: }
270: boolean hasCandidate = false;
271: Object candidate = null;
272: for (Iterator it = collection.iterator(); it.hasNext();) {
273: Object elem = it.next();
274: if (!hasCandidate) {
275: hasCandidate = true;
276: candidate = elem;
277: } else if (candidate != elem) {
278: return false;
279: }
280: }
281: return true;
282: }
283:
284: }
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