获取月初和月末

package com.chryl.test;

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

/**
 * 获取月初和月末
 */
public class Test5 {

    public static void main(String[] args) throws Exception {
        getFirstAndLastDayOfMonth("2019-02-15");
        getFirstAndLastDayOfLastMonth();

    }

    /**
     * 获取当前日期的上月月初和月末
     */
    public static void getFirstAndLastDayOfLastMonth() {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        //获取前一个月第一天
        Calendar calendar1 = Calendar.getInstance();
        calendar1.add(Calendar.MONTH, -1);
        calendar1.set(Calendar.DAY_OF_MONTH, 1);
        String firstDay = sdf.format(calendar1.getTime());
        System.out.println(firstDay);
        Date time = calendar1.getTime();
        System.out.println(time);
        //获取前一个月最后一天
        Calendar calendar2 = Calendar.getInstance();
        calendar2.set(Calendar.DAY_OF_MONTH, 0);
        String lastDay = sdf.format(calendar2.getTime());
        System.out.println(lastDay);
        Date time1 = calendar2.getTime();
        System.out.println(time1);

    }


    /**
     * 获取指定日期的月初和月末
     *
     * @throws Exception
     */
    public static void getFirstAndLastDayOfMonth(String date_str) throws Exception {

        Calendar cale = Calendar.getInstance();

        SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");

        cale.setTime(formatter.parse(date_str));

        cale.add(Calendar.MONTH, 0);

        cale.set(Calendar.DAY_OF_MONTH, 1);

        String firstDayOfMonth = formatter.format(cale.getTime()); // 当月第一天 2019-02-01
        System.out.println(firstDayOfMonth);

        cale.add(Calendar.MONTH, 1);

        cale.set(Calendar.DAY_OF_MONTH, 0);

        String lastDayOfMonth = formatter.format(cale.getTime()); // 当月最后一天 2019-02-28
        System.out.println(lastDayOfMonth);

        System.out.println("===================");
    }

}