List集合处理

package com.zhengqing.demo.ListUtil;

import com.alibaba.fastjson.JSONObject;

import java.math.BigDecimal;
import java.util.*;
import java.util.stream.Collectors;

public class ListUtil {

    /**
     * 集合分组
     *
     * @param list      分组集合
     * @param groupName 分组key
     * @return
     */
    public static <T> Map<String, List<T>> groupList(List<T> list, String groupName) {
        return list.stream().collect(Collectors.groupingBy(e -> JSONObject.parseObject(JSONObject.toJSONString(e), Map.class).get(groupName).toString()));
    }

    /**
     * 集合求和
     *
     * @param list    分组集合
     * @param sumName 求和key
     * @return
     */
    public static <T> BigDecimal sumList(List<T> list, String sumName) {
        List<Map> maps = JSONObject.parseArray(JSONObject.toJSONString(list), Map.class);
        return maps.stream().map(e -> new BigDecimal(String.valueOf(e.get(sumName)))).reduce(BigDecimal.ZERO, BigDecimalUtils::sum);
    }

    /**
     * 集合过滤
     *
     * @param list     过滤集合
     * @param filtName 过滤属性
     * @param values   过滤值集合
     * @param tClass   返回值类型
     * @return
     */
    public static <T> List<T> filtList(List<T> list, String filtName, List<Object> values, Class<T> tClass) {
        List<Map> maps = JSONObject.parseArray(JSONObject.toJSONString(list), Map.class);
        for (Object value : values) {
            maps = maps.stream().filter(a -> !a.get(filtName).equals(value)).collect(Collectors.toList());
        }
        return JSONObject.parseArray(JSONObject.toJSONString(maps), tClass);
    }

    /**
     * 集合去重
     *
     * @param list   去重集合
     * @param keys   去重key
     * @param tClass 返回值类型
     * @param 
     * @return
     */
    public static <T> List<T> distinctByKey(List<T> list, List<String> keys, Class<T> tClass) {
        List<Map> maps = JSONObject.parseArray(JSONObject.toJSONString(list), Map.class);
        for (String key : keys) {
            maps = maps.stream().collect(Collectors.collectingAndThen(
                    Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(p -> String.valueOf(p.get(key))))),
                    ArrayList::new));
        }
        return JSONObject.parseArray(JSONObject.toJSONString(maps), tClass);
    }
    /**
     * 集合空检测
     * @param list
     * @param 
     * @return
     */
    public static <T> boolean isEmpty(List<T> list) {
        return null == list || 0 == list.size();
    }

    /**
     * 集合空检测
     * @param list
     * @param 
     * @return
     */
    public static <T> boolean isNotEmpty(List<T> list) {
        return !isEmpty(list);
    }

    public static void main(String[] args) {
        List<Map> list = new ArrayList<>();
        int i = 5;
        for (int i1 = 0; i1 < i; i1++) {
            Map user = new HashMap();
            user.put("id", i1);
            user.put("age", i1);
            user.put("name", "v");
            if (i1 > 3) {
                user.put("name", "k");
            }
            list.add(user);
        }
        Map<String, List<Map>> age = groupList(list, "age");
        System.out.println("age = " + JSONObject.toJSONString(age));
        BigDecimal age1 = sumList(list, "age");
        System.out.println("age = " + age1);
        List<Object> objects = new ArrayList<>();
        objects.add(1);
        objects.add(2);
        List<Map> id = filtList(list, "id", objects, Map.class);
        id.forEach(System.out::println);;
        List objects1 = new ArrayList<>();
        objects1.add("name");
        List<Map> objects2 = distinctByKey(list, objects1, Map.class);
        objects2.forEach(System.out::println);
    }

}

package com.zhengqing.demo.ListUtil;

import java.math.BigDecimal;

public class BigDecimalUtils {

    public static BigDecimal ifNullSet0(BigDecimal in) {
        if (in != null) {
            return in;
        }
        return BigDecimal.ZERO;

    }

    public static BigDecimal sum(BigDecimal... in) {
        BigDecimal result = BigDecimal.ZERO;
        for (int i = 0; i < in.length; i++) {
            result = result.add(ifNullSet0(in[i]));
        }
        return result;

    }

}