拓展集合工具类CollectionUtils，供大家参考，具体内容如下
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package com.demo.utils;import java.lang.reflect.Method;import java.util.ArrayList;import java.util.Collection;import java.util.HashSet;import java.util.Iterator;import java.util.LinkedHashMap;import java.util.LinkedHashSet;import java.util.List;import java.util.Map;import java.util.Set;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import com.demo.bean.EmployeeEntity;/** * * <p>自定义集合工具类拓展常用方法</p> * @autho 董杨炀 * @time 2017-4-10 上午11:33:36 */public class CollectionUtils extends org.apache.commons.collections.CollectionUtils { private static final Logger LOGGER = LoggerFactory.getLogger(CollectionUtils.class); private static final int DEFAULT_SIZE = 1000; /** * * <p>拆分List为固定大小的多个集合</p> * <p>推荐使用</p> * <p>返回集合的size越小,此方法性能越高</p> * @param baseList * @param size * @return ArrayList * @autho 董杨炀 * @time 2017-4-10 上午11:30:43 */ @SuppressWarnings("unchecked") public static <T> List<List<T>> fastSplitList(List<T> baseList, int size) { if (baseList == null || baseList.size() == 0) { return null; } if (size <= 0) { size = DEFAULT_SIZE; } int arrSize = baseList.size() % size == 0 ? baseList.size() / size : baseList.size() / size + 1; List<List<T>> resultList = new ArrayList<List<T>>(); for (int i = 0; i < arrSize; i++) { if (arrSize - 1 == i) { resultList.add((List<T>) new ArrayList<Object>( baseList.subList(i * size, baseList.size()))); } else { resultList.add((List<T>) new ArrayList<Object>( baseList.subList(i * size, size * (i + 1)))); } } return resultList; } /** * * <p>拆分List为固定大小的多个集合</p> * <p>返回集合的size越大,此方法性能越高</p> * @param baseList * @param size * @return ArrayList * @autho 董杨炀 * @time 2017-4-10 上午11:30:43 */ public static <T> List<List<T>> splitList(List<T> baseList, int size) { if (baseList == null || baseList.size() == 0) { return null; } if (size <= 0) { size = DEFAULT_SIZE; } List<List<T>> resultList = new ArrayList<List<T>>(); for (int i = 0; i < baseList.size(); ++i) { if (i % size == 0) { List<T> result = new ArrayList<T>(); resultList.add(result); } resultList.get(i / size).add(baseList.get(i)); } return resultList; } /** * * <p>集合转Set</p> * @param coll 源集合 * @param keyType 属性类型 * @param keyMethodName 属性get方法 * @return LinkedHashSet * @autho 董杨炀 * @time 2017-4-10 上午11:31:50 */ public static <K, V> Set<K> asSet(final java.util.Collection<V> coll,final Class<K> keyType ,final String keyMethodName) { if (CollectionUtils.isEmpty(coll)) { return new HashSet<K>(0); } final Set<K> set = new LinkedHashSet<K>(coll.size()); try { for (final V value : coll) { Object object; Method method = value.getClass().getMethod(keyMethodName); object = method.invoke(value); @SuppressWarnings("unchecked") final K key = (K) object; set.add(key); } } catch (Exception e) { LOGGER.error(e.getMessage(), e); throw new CollectionUtilsException("Collection conversion Set exceptions"); } return set; } /** * * <p>集合转Map</p> * <p>比如:List<EmployeeEntity>,讲EmployeeEntity的name属性作为key,转换成Map</p> * @param coll 源集合 * @param keyType 属性类型 * @param valueType 源数据类型(实体类型) * @param keyMethodName 属性get方法 * @return LinkedHashMap * @autho 董杨炀 * @time 2017-4-10 上午11:32:01 */ public static <K, V> Map<K, V> asMap(final java.util.Collection<V> coll,final Class<K> keyType ,final Class<V> valueType,final String keyMethodName) { if (CollectionUtils.isEmpty(coll)) { return new LinkedHashMap<K, V>(0); } final Map<K, V> map = new LinkedHashMap<K, V>(coll.size()); try { Method method = valueType.getMethod(keyMethodName); for (final V value : coll) { Object object; object = method.invoke(value); @SuppressWarnings("unchecked") final K key = (K) object; map.put(key, value); } } catch (Exception e) { LOGGER.error(e.getMessage(), e); throw new CollectionUtilsException("Collection conversion Map exceptions"); } return map; } /** * * <p>集合转List</p> * @param coll * @return ArrayList * @autho 董杨炀 * @time 2017-4-10 上午11:32:56 */ public static <V> List<V> asList(final java.util.Collection<V> coll) { if (CollectionUtils.isEmpty(coll)) { return new ArrayList<V>(0); } final List<V> list = new ArrayList<V>(); for (final V value : coll) { if (value != null) { list.add(value); } } return list; } /** * <p>集合<String>toString</p> * @param collection 泛型必须为String类型 * @param split 比如连接符"," * @return * @autho 董杨炀 * @time 2017-4-10 下午3:22:24 */ public static String collToString(Collection<String> collection, String split) { StringBuilder sb = new StringBuilder(); if (collection != null) { int i = 0, size = collection.size(); for (Iterator<String> iterator = collection.iterator(); iterator.hasNext();) { String str = iterator.next(); sb.append(str); if (++i < size) { sb.append(split); } } } return sb.toString(); } static class CollectionUtilsException extends RuntimeException{ private static final long serialVersionUID = 1L; public CollectionUtilsException(String s) { super(s); } public CollectionUtilsException(String s, Throwable e) { super(s, e); } public CollectionUtilsException(Throwable e) { super(e); } } public static void main(String[] args) { List<String> baseList = new ArrayList<String>(1000000); for (int i = 0; i < 1000000; i++) { baseList.add("data:"+" i"); } long currentTimeMillis1 = System.currentTimeMillis(); List<List<String>> splitList = splitList(baseList, 1000); long currentTimeMillis2 = System.currentTimeMillis(); System.out.println(splitList.size()); System.out.println("切割完成时间为:"+String.valueOf(currentTimeMillis2-currentTimeMillis1)+"毫秒"); long currentTimeMillis3 = System.currentTimeMillis(); List<List<String>> newList = fastSplitList(baseList,1000); long currentTimeMillis4 = System.currentTimeMillis(); System.out.println(newList.size()); System.out.println("快速切割完成时间为:"+String.valueOf(currentTimeMillis4-currentTimeMillis3)+"毫秒"); List<EmployeeEntity> employeeList = new ArrayList<EmployeeEntity>(); for (int i = 1; i < 11; i++) { EmployeeEntity entity = new EmployeeEntity(); entity.setName("名字"+String.valueOf(i)); employeeList.add(entity); } System.out.println(employeeList.size()); Set<String> set = CollectionUtils.asSet(employeeList, String.class, "getName"); for (String name : set) { System.out.println(name); } Map<String, EmployeeEntity> map = CollectionUtils.asMap(employeeList, String.class, EmployeeEntity.class, "getName"); Set<String> keySet = map.keySet(); for (String key : keySet) { System.out.println(key); System.out.println(map.get(key)); } List<EmployeeEntity> list = CollectionUtils.asList(map.values()); for (EmployeeEntity employeeEntity : list) { System.out.println(employeeEntity); 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原文链接：https://blog.csdn.net/qq_35712358/article/details/70254565
