Java对集合的操作方法

1. 数组转集合

//数组转集合
String[] split = quickRechargeAmount.split(",");
List<String> stringList = Stream.of(split).collect(Collectors.toList());

2. 对List集合数据内容进行分组

//对List集合数据内容进行分组
Map<String, List<LiveAppGiftResponse>> collectList = giftResponseList.stream().collect(Collectors.groupingBy(LiveAppGiftResponse::getGiftTypeName));

3. 匹配两个集合内相等的元素，生成新的集合

//匹配两个集合内相等的元素，生成新的集合
private List<AppLiveUserRankResponse> getUserRankInfo(List<LiveUserRankCache> dayRankCacheList, Integer anchorId) {List<AppLiveUserInfoResponse> userRewardList = appLiveRewardMapper.getUserRewardList(CommonContext.get().getSiteId(), anchorId);if (CollectionTool.isNotEmpty(dayRankCacheList) && CollectionTool.isNotEmpty(userRewardList)) {//组装用户与排行榜信息List<AppLiveUserRankResponse> userRankList = dayRankCacheList.stream().map(dayRankCache -> userRewardList.stream().filter(userReward -> Objects.equals(userReward.getUserId(), dayRankCache.getUserId())).findFirst().map(m -> {AppLiveUserRankResponse appLiveUserRank = new AppLiveUserRankResponse();appLiveUserRank.setRank(dayRankCache.getRank());appLiveUserRank.setScore(dayRankCache.getScore());appLiveUserRank.setAvatarUrl(m.getAvatarUrl());appLiveUserRank.setNickName(m.getNickName());return appLiveUserRank;}).orElse(null)).filter(Objects::nonNull).collect(Collectors.toList());return userRankList;}return null;
}

4. 根据A集合某元素去对比B集合某元素，生成过滤后的B集合

//根据A集合某元素去对比B集合某元素，生成过滤后的B集合
public List<User> selectUnassignedGameList(List<User> userBList) {// 查询所有用户信息List<User> userAList = this.list();// 获取userBList的中所有用户信息并对比后排除userAList已存在用户信息List<User> list = userBList.stream().filter(b -> !userAList.stream().map(a-> a.getUId()).collect(Collectors.toList()).contains(b.getUId())).collect(Collectors.toList());return list;}

5. 集合内某一元素比对特定条件进行排序

        //查询当前账户币种信息集合List<LiveCustomerWallet> customerWalletList = customerWalletMapper.search(Criteria.add(LiveCustomerWallet.PROP_CUSTOMER_ID, Operator.EQ, model.getUserId()), Order.asc(LiveCustomerWallet.PROP_CURRENCY));if (CollectionTool.isNotEmpty(customerWalletList)){//先按指定币种排序，然后再主货币排序，再按币种排序String mainCurrency = BaseCacheTool.getSysSite(model.getSiteId()).getMainCurrency();if (!mainCurrency.equals(model.getCurrency())){customerWalletList.sort((o1, o2) -> {int i = o1.getCurrency().equals(mainCurrency) ? 0 : 1;int i2 = o2.getCurrency().equals(mainCurrency) ? 0 : 1;return i - i2;});}customerWalletList.sort((o1, o2) -> {int i = o1.getCurrency().equals(model.getCurrency()) ? 0 : 1;int i2 = o2.getCurrency().equals(model.getCurrency()) ? 0 : 1;return i - i2;});}

6. 集合去重

//使用java steam进行去重
List<Integer> list = numbersList.stream().distinct().collect(Collectors.toList());//将重复的列表添加到 LinkedHashSet，然后将内容返回到列表中
LinkedHashSet<Integer> hashSet = new LinkedHashSet<>(numbersList);

7. 对集合进行分页并模糊查询

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;public class ListTest {public static void main(String[] args) {List<User> list = new ArrayList<>();list.add(new User("zhangsan", 18));list.add(new User("lisi", 19));list.add(new User("wangwu", 20));list.add(new User("zhaoliu", 21));String searchName = "h";// 是否全部匹配,还是 局部包含匹配Boolean globalMatch = Boolean.FALSE;//获取当前页int pageNumber = 1;//一页返回多少条int pageSize = 2;List<User> stringList = list.stream().filter(l -> globalMatch?l.getName().equals(searchName):l.getName().contains(searchName))//根据年龄升序排序.sorted(Comparator.comparing(User::getAge)).collect(Collectors.toList());//一页 返回二条List<User> pageList = stringList.stream().skip((pageNumber-1)*pageSize).limit(pageSize).collect(Collectors.toList());System.out.println("返回总条数:"+stringList.size()+"当前页为:"+pageNumber+"每页显示条数:"+pageSize);System.out.println("本次返回的数据为:");pageList.forEach(System.out::println);}
}
class User{private String name;private Integer age;public User(String name, Integer age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}@Overridepublic String toString() {return "User{" +"name='" + name + '\'' +", age=" + age +'}';}
}