问如何使用php将字符串日期列表插入到mysql中？

EN

List<Date> dates = getDates(mDate, mDate2);

private static List<Date> getDates(String dateString1, String dateString2)
{
    ArrayList<Date> dates = new ArrayList<Date>();
    DateFormat df1 = new SimpleDateFormat("yyyy-MM-dd");

    Date date1 = null;
    Date date2 = null;

    try {
        date1 = df1 .parse(dateString1);
        date2 = df1 .parse(dateString2);
    } catch (ParseException e) {
        e.printStackTrace();
    }

    Calendar cal1 = Calendar.getInstance();
    cal1.setTime(date1);


    Calendar cal2 = Calendar.getInstance();
    cal2.setTime(date2);

    while(!cal1.after(cal2))
    {
        dates.add(cal1.getTime());
        cal1.add(Calendar.DATE, 1);
    }
    return dates;
}

String customername = getPpname();
String customerroom = getRrname();
String customerid = getRrid();

private static class MYTASK {
    List<Date> dates;
    String customername;
    String customerroom;
    String customerid;

    MYTASK(List<Date> dates, String customername, String customerroom, String customerid) {
        this.dates = dates;
        this.customername = customername;
        this.customerroom = customerroom;
        this.customerid = customerid;
    }
}

MYTASK params = new MYTASK(dates, customername, customerroom,customerid);
        JSONTask_ListDates jsonTaskListDates = new JSONTask_ListDates();
        jsonTaskListDates.execute(params);

class JSONTask_ListDates extends AsyncTask<MYTASK, Void, Void> {

    @Override
    protected void onPreExecute() {
        /* rlllogin.setVisibility(View.VISIBLE);*/
    }
    @Override
    protected void doInBackground(MYTASK... params) {
        String urlreserve = "http://alar-regulations.000webhostapp.com/reservation_insert_date.php";

        String id = params[3].customerid;
        String rname = params[1].customerroom;
        String pname = params[2].customername;
        List<Date> dates = params[0].dates;


        try {
            URL url = new URL(urlreserve);
            HttpURLConnection httpURLConnection = (HttpURLConnection)url.openConnection();
            httpURLConnection.setRequestMethod("POST");
            httpURLConnection.setDoOutput(true);
            //new
            httpURLConnection.setDoInput(true);
            OutputStream OS = httpURLConnection.getOutputStream();
            BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(OS, "UTF-8"));

            String data = URLEncoder.encode("id", "UTF-8")+"="+URLEncoder.encode(id, "UTF-8")+"&"
                    +URLEncoder.encode("rname", "UTF-8")+"="+URLEncoder.encode(rname, "UTF-8")+"&"
                    +URLEncoder.encode("pname", "UTF-8")+"="+URLEncoder.encode(pname, "UTF-8")+"&"
                    +URLEncoder.encode("dates", "UTF-8")+"="+URLEncoder.encode(dates, "UTF-8");

            bufferedWriter.write(data);
            bufferedWriter.flush();
            bufferedWriter.close();
            OS.close();
            InputStream IS = httpURLConnection.getInputStream();
            //new
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(IS, "iso-8859-1"));
            String response ="";
            String line = "";
            while ((line = bufferedReader.readLine()) !=null) {
                response+=line;
            }
            bufferedReader.close();
            IS.close();
            return response;

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
    @Override
    protected void onPostExecute(Void result) {
        /*pDialog.dismiss();*/
        /* rlllogin.setVisibility(View.GONE);*/
        Intent intent = new Intent(Booking.this, Reservation_List.class);
        startActivity(intent);
        Booking.this.finish();
        /* dialog2.dismiss();*/
    }
}

wrong first argument type found java.util.list required java.lang string

            <?php
require "connection.php";

$res_rname= $_POST["rname"];
$res_per_name= $_POST["pname"];
$res_id= $_POST["id"];
$dates= $_POST["dates"];
$sql_query = "Insert into res_event_table ( res_id, res_check_in_out, 
res_room_name, res_name) values ( '$res_id','$val', '$res_rname', 
'$res_per_name')";

if($dates>0)
 {
    foreach($dates as $val){
        $result = mysqli_query($conn ,$sql_query);
            if (!$result){
            echo "failed" .mysqli_connect_error;
            }else{
            echo "Reservation Success";
         }
       }
    }

 ?>