java8 list新特性

import com.google.common.collect.Lists;

import java.math.BigDecimal;
import java.util.*;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Collectors;
import java.util.concurrent.ConcurrentHashMap;

import static java.util.stream.Collectors.collectingAndThen;
import static java.util.stream.Collectors.toCollection;
import static java.util.Comparator.comparingLong;;

public class test {

    public void test(){
        List<UserDomain> list = Lists.newArrayList();
        //判断对象属性去重
        long count = list.stream().filter(distinctByKey(UserDomain :: getUserName)).distinct().count();
        if(count < list.size()){

        }

        //根据对象属性去重
        list = list.stream().collect(
                collectingAndThen(toCollection(() -> new TreeSet<>(comparingLong(UserDomain::getId))), ArrayList::new)
        );
        //去重
        list = list.stream().distinct().collect(Collectors.toList());

        //排序
        list.sort(Comparator.comparing(UserDomain::getUserName));
        list.sort(Comparator.comparing(UserDomain::getUserName).reversed());
        list = list.stream().sorted(Comparator.comparing(UserDomain::getUserName, Comparator.nullsFirst(Comparator.naturalOrder()))).collect(Collectors.toList());
        list = list.stream().sorted(Comparator.comparing(UserDomain::getUserName, Comparator.nullsFirst(Comparator.naturalOrder())).reversed()).collect(Collectors.toList());

        //过滤
        list = list.stream().filter(a -> a.getUserName().equals("张三")).collect(Collectors.toList());

        //求和
        BigDecimal totalMoney = list.stream().map(UserDomain::getUnitPrice).reduce(BigDecimal.ZERO, BigDecimal::add);

        //遍历(使用return可以达到continue的效果)
        list.forEach(userList -> {
            return;
        });
        //groupBy分组
        Map<Long, List<UserDomain>> groupBy = list.stream().collect(Collectors.groupingBy(UserDomain::getId));

        //id为key，对象为value转Map
        Map<Long,UserDomain> userMap = list.stream().collect(Collectors.toMap(UserDomain::getId, a -> a,(k1,k2)->k1));
        //去重
        userMap = list.stream().collect(Collectors.toMap(UserDomain::getId, user -> user,(k1,k2)->k1));
        //JSONArray.toJSONString(userMap);
        
        //获取对象list中某个属性的值的lis
        List<String> nameList = list.stream().map(UserDomain::getUserName).collect(Collectors.toList());
        List<String> nameList1 = list.stream().map(e -> e.getUserName()).collect(Collectors.toList());
        
        
    }


    private static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {
        Map<Object, Boolean> seen = new ConcurrentHashMap<>();
        return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
    }

}