//本月
    @Test
    public void test01() {
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
        Calendar c = Calendar.getInstance();
        c.add(Calendar.MONTH, 0);
        c.set(Calendar.DAY_OF_MONTH, 1);//1:本月第一天
        String day1 = format.format(c.getTime());
        System.out.println("本月第一天:" + day1);
        //获取当前月最后一天
        Calendar ca = Calendar.getInstance();
        ca.set(Calendar.DAY_OF_MONTH, ca.getActualMaximum(Calendar.DAY_OF_MONTH));
        String day2 = format.format(ca.getTime());
        System.out.println("本月最后一天:" + day2);
    }

    //获取上个月的第一天
    @Test
    public void test02() {
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
        Calendar calendar = Calendar.getInstance();
        calendar.add(Calendar.MONTH, -1);
        calendar.set(Calendar.DAY_OF_MONTH, 1);
        System.out.println("上个月第一天：" + format.format(calendar.getTime()));
    }

    //获取上个月的最后一天
    @Test
    public void test03() {
        SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd");
        Calendar calendar = Calendar.getInstance();
        int month = calendar.get(Calendar.MONTH);
        calendar.set(Calendar.MONTH, month - 1);
        calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH));
        System.out.println("上个月最后一天：" + sf.format(calendar.getTime()));

    }