import java.text.DateFormat;

import java.text.SimpleDateFormat;

import java.util.Date;

public class ConsoleTest {

    public static void main(String args[]) {

        String str = "20200402150221";

        DateFormat df1 = new SimpleDateFormat("yyyyMMddHHmmss");

        DateFormat df2 = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

        try {

            Date time1 = df1.parse(str);

            String time2 = df2.format(time1);

            System.out.println(time2);

        } catch (Exception e) {

            System.out.println(e.getMessage());

        }

    }

}

        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyyMMddHHmmss");

        LocalDateTime ldt = LocalDateTime.parse(datetime,dtf);

        DateTimeFormatter fa = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");

        String datetime2 = ldt.format(fa);

public static String strToDateFormat(String date) throws ParseException{

           SimpleDateFormat formatter = new SimpleDateFormat("yyyyMMddHHmmss");

           formatter.setLenient(false);

           Date newDate= formatter.parse(date);

           formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

           return formatter.format(newDate);

       }