How to convert christian year to thai year in Java?

you can use ThaiBuddhistDate class in package - java.time.chrono

you can use below example for reference -

    public class Test {


    public static void main(String[] args) {

        String date = "2020-12-31 20:08:00";
        // Convert Thai Buddhist date to ISO date

        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-mm-dd HH:MM:ss");
        try {
            ThaiBuddhistDate thaiBuddhistNow = ThaiBuddhistDate.from(LocalDate.parse(date,formatter));
            System.out.println("Thai  Buddhist Current Date  from  ISO:  "
                    + thaiBuddhistNow);
        }catch (Exception e){
            e.printStackTrace();
        }
    }
}