String to Date format string For java

    @SuppressLint("SimpleDateFormat")
    public static String toDateFormat(String v) {
        String rtn = "";
        if ( StringUtils.isNotEmpty(v) ) {
            v = v.replaceAll("[^0-9]", "");
            System.out.println(v);
            SimpleDateFormat pm = new SimpleDateFormat("yyyyMMdd");
            SimpleDateFormat sm = new SimpleDateFormat("yyyy-MM-dd");
            try {
                Date vd = pm.parse(v);
                rtn = sm.format(vd);
            } catch (ParseException e) {
                e.printStackTrace();
            }
            System.out.println(rtn);
        } else {
        }
        return rtn;
    }