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/*
 * Copyright 2002-2013 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
 *
 *      http://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;

/**
 * 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 true if the supplied Collection is null
	 * or empty. Otherwise, return false.
	 * @param collection the Collection to check
	 * @return whether the given Collection is empty
	 */
	public static boolean isEmpty(Collection collection) {
		return (collection == null || collection.isEmpty());
	}

	/**
	 * Return true if the supplied Map is null
	 * or empty. Otherwise, return false.
	 * @param map the Map to check
	 * @return whether the given Map is empty
	 */
	public static boolean isEmpty(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.
	 * 

A null source value will be converted to an * empty List. * @param source the (potentially primitive) array * @return the converted List result * @see org.springframework.util.ObjectUtils#toObjectArray(Object) */ public static List arrayToList(Object source) { return Arrays.asList(ObjectUtils.toObjectArray(source)); } /** * Merge the given array into the given Collection. * @param array the array to merge (may be null) * @param collection the target Collection to merge the array into */ @SuppressWarnings("unchecked") public static void mergeArrayIntoCollection(Object array, Collection collection) { if (collection == null) { throw new IllegalArgumentException("Collection must not be null"); } Object[] arr = ObjectUtils.toObjectArray(array); for (Object elem : arr) { collection.add(elem); } } /** * 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. * @param props the Properties instance to merge (may be null) * @param map the target Map to merge the properties into */ @SuppressWarnings("unchecked") public static void mergePropertiesIntoMap(Properties props, Map map) { if (map == null) { throw new IllegalArgumentException("Map must not be null"); } if (props != null) { for (Enumeration en = props.propertyNames(); en.hasMoreElements();) { String key = (String) en.nextElement(); Object value = props.getProperty(key); if (value == null) { // Potentially a non-String value... value = props.get(key); } map.put(key, value); } } } /** * Check whether the given Iterator contains the given element. * @param iterator the Iterator to check * @param element the element to look for * @return true if found, false else */ public static boolean contains(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 true if found, false else */ public static boolean contains(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 * true for an equal element as well. * @param collection the Collection to check * @param element the element to look for * @return true if found, false else */ public static boolean containsInstance(Collection collection, Object element) { if (collection != null) { for (Object candidate : collection) { if (candidate == element) { return true; } } } return false; } /** * Return true if any element in 'candidates' is * contained in 'source'; otherwise returns 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 'candidates' that is contained in * 'source'. If no element in 'candidates' is present in * 'source' returns null. Iteration order is * {@link java.util.Collection} implementation specific. * @param source the source Collection * @param candidates the candidates to search for * @return the first present object, or null if not found */ public static Object findFirstMatch(Collection source, Collection candidates) { if (isEmpty(source) || isEmpty(candidates)) { return null; } for (Object candidate : candidates) { if (source.contains(candidate)) { return 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 null if none or more than one such value found */ @SuppressWarnings("unchecked") public static T findValueOfType(Collection collection, 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 null if none or more than one such value found */ 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 true if the collection contains a single reference or * multiple references to the same instance, false else */ 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 null if no clear * common type has been found (or the collection was empty) */ 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; } /** * 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 enumeration to an iterator. * @param enumeration the enumeration * @return the iterator */ public static Iterator toIterator(Enumeration enumeration) { return new EnumerationIterator(enumeration); } /** * Iterator wrapping an Enumeration. */ private static class EnumerationIterator implements Iterator { private Enumeration enumeration; public EnumerationIterator(Enumeration enumeration) { this.enumeration = enumeration; } public boolean hasNext() { return this.enumeration.hasMoreElements(); } public E next() { return this.enumeration.nextElement(); } public void remove() throws UnsupportedOperationException { throw new UnsupportedOperationException("Not supported"); } } }





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