Java获得当前日期和前后几天日期

if (startTime == null || startTime.length() == 0 || endTime == null || endTime.length() == 0) {    // 获得当前日期    SimpleDateFormat df = new SimpleDateFormat("yyyyMMdd"); //设置日期格式    Date nowDate = new Date();    String nowTime = df.format(nowDate); // 20170410    // 获得前5天的日期    Calendar now = Calendar.getInstance();    now.setTime(nowDate);    now.set(Calendar.DATE, now.get(Calendar.DATE) - 5);    Date preDate = now.getTime();    String preTime = df.format(preDate); // 20170405    startTime = preTime; // 20170405    endTime = nowTime; // 20170410}