//获取当前月第一天:
Calendar c = Calendar.getInstance();
c.add(Calendar.MONTH, 0);
c.set(Calendar.DAY_OF_MONTH,1);//设置为1号,当前日期既为本月第一天
String first = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(c.getTime());
System.out.println("本月第一天 :"+first);
//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 last = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(ca.getTime());
System.out.println("本月最后一天 :"+last);
Calendar cals1 = new GregorianCalendar();
//获取这个星期的第一天
cals1.setFirstDayOfWeek(Calendar.MONDAY);
//将时间的时分秒 写死
//小时
cals1.set(Calendar.HOUR_OF_DAY, 0);
//分钟
cals1.set(Calendar.MINUTE, 0);
//秒
cals1.set(Calendar.SECOND, 0);
//获取取本周的星期一的时间
cals1.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
String format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(cals1.getTime().clone());
System.out.println(format);