Java tutorial
/* * Copyright 2002-2010 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 com.wcs.base.util; import java.util.Arrays; import java.util.Collection; import java.util.Enumeration; import java.util.Iterator; import java.util.List; import java.util.Map; import java.util.Properties; /** * Miscellaneous collection utility methods. * Mainly for internal use within the framework. * * @author Juergen Hoeller * @author Rob Harrop * @since 1.1.3 */ public abstract class CollectionUtils extends org.apache.commons.collections.CollectionUtils { /** * Return <code>true</code> if the supplied Collection is <code>null</code> * or empty. Otherwise, return <code>false</code>. * @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 <code>true</code> if the supplied Map is <code>null</code> * or empty. Otherwise, return <code>false</code>. * @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. * <p>A <code>null</code> source value will be converted to an * empty List. * @param source the (potentially primitive) array * @return the converted List result * @see 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 <code>null</code>) * @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. * <p>Uses <code>Properties.propertyNames()</code> to even catch * default properties linked into the original Properties instance. * @param props the Properties instance to merge (may be <code>null</code>) * @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 <code>true</code> if found, <code>false</code> 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 <code>true</code> if found, <code>false</code> 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. * <p>Enforces the given instance to be present, rather than returning * <code>true</code> for an equal element as well. * @param collection the Collection to check * @param element the element to look for * @return <code>true</code> if found, <code>false</code> else */ public static boolean containsInstance(Collection collection, Object element) { if (collection != null) { for (Object candidate : collection) { if (candidate == element) { return true; } } } return false; } /** * Return <code>true</code> if any element in '<code>candidates</code>' is * contained in '<code>source</code>'; otherwise returns <code>false</code>. * @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</code>' that is contained in * '<code>source</code>'. If no element in '<code>candidates</code>' is present in * '<code>source</code>' returns <code>null</code>. 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</code> 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 <code>null</code> if none or more than one such value found */ @SuppressWarnings("unchecked") public static <T> T findValueOfType(Collection<?> collection, 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</code> 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 <code>true</code> if the collection contains a single reference or * multiple references to the same instance, <code>false</code> 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 <code>null</code> 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; } /** * Adapts an enumeration to an iterator. * @param enumeration the enumeration * @return the iterator */ public static <E> Iterator<E> toIterator(Enumeration<E> enumeration) { return new EnumerationIterator<E>(enumeration); } /** * Iterator wrapping an Enumeration. */ private static class EnumerationIterator<E> implements Iterator<E> { private Enumeration<E> enumeration; public EnumerationIterator(Enumeration<E> 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"); } } }