1.SimpleDateFormat simDate= new SimpleDateFormat("yyyyMM");
Date date = simDate.parse(“201809”);
Calendar cal=Calendar.getInstance();
cal.setTime(date);
cal.add(cal.MONTH,-1);
Date time = cal.getTime()
String endMonth = simDate.format(time);
得到的是月份减去一的
2.SimpleDateFormat s= new SimpleDateFormat("yyyy年MM月dd日");
Date stDate= s.parse(date);
SimpleDateFormat simDate= new SimpleDateFormat("yyyyMMdd");
String format = simDate.format(stDate);
将2018年09月08日转换为20180908