JAVA获取本月的第一天和最后一天

//获取本月第一天

Calendar calendar = Calendar.getInstance();
calendar.add(Calendar.MONTH, 0);
calendar.set(Calendar.DAY_OF_MONTH, 1);
return calendar.getTime();

//获取本月最后一天

Calendar calendar = Calendar.getInstance();
calendar.add(Calendar.MONTH, 1);
calendar.set(Calendar.DAY_OF_MONTH, 0);

//获取上个月第一天

Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.MONDAY, calendar.get(Calendar.MONDAY) - 1);
calendar.set(Calendar.DAY_OF_MONTH, 1);

//获取上月最后一天

Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.MONDAY, calendar.get(Calendar.MONDAY) - 1);
calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH));

//自定义时间

SimpleDateFormat format= new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

String startTime = "2019-12-16 23:59:59";

Date startDate = format.parse(startTime)