java8 集合分组（根据集合中对象中时间字段的月份分组）

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);
    }