java8 集合分组（根据集合中对象中时间字段的月份分组）

待我称王封你为后i 2023-06-11 05:29 32阅读 0赞

简单带时间字段类

package com.xxxxx.entity;
    
    import java.time.LocalDate;
    import lombok.Data;
    import lombok.EqualsAndHashCode;
    import lombok.experimental.Accessors;
    
    /**
     * @author zws
     * @since 2019-10-11
     */
    @Data
    @EqualsAndHashCode(callSuper = true)
    @Accessors(chain = true)
    public class BsUpholdOrder extends BaseEntity {
    
        private static final long serialVersionUID = 1L;
    
        /**
         * 保养日期
         */
        private LocalDate upholdDate;
    
        /**
         * 实际保养人
         */
        private String upholdPerson;
    
    
    }

BaseEntity 只是一个id 分页参数公共类，要不要无所谓。

骚操作开始：

public static void main(String[] args) {
            List<BsUpholdOrder> orders = new ArrayList<>();
            BsUpholdOrder order1 = new BsUpholdOrder();
            order1.setUpholdPerson("张三1");
            order1.setUpholdDate(LocalDate.now());
            BsUpholdOrder order2 = new BsUpholdOrder();
            order2.setUpholdPerson("张三2");
            order2.setUpholdDate(LocalDate.now().withMonth(9));
            BsUpholdOrder order3 = new BsUpholdOrder();
            order3.setUpholdPerson("张三3");
            order3.setUpholdDate(LocalDate.now());
            BsUpholdOrder order4 = new BsUpholdOrder();
            order4.setUpholdPerson("张三4");
            order4.setUpholdDate(LocalDate.now().withMonth(8));
            orders.add(order1);
            orders.add(order2);
            orders.add(order3);
            orders.add(order4);
    
            //分组 按月
            Map<Integer,List<BsUpholdOrder>> groupByMonth = orders.stream().collect(Collectors.groupingBy(o -> o.getUpholdDate().getMonthValue()));
            System.out.println(groupByMonth);
        }