import java.time.OffsetDateTime;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeFormatterBuilder;
import java.util.Locale;

class Main {
    public static void main(String[] args) {
        String strDateTime = "2020-08-21T14:00:00.00+0700";

        // Recommended
        DateTimeFormatter dtf = new DateTimeFormatterBuilder()
                                .append(DateTimeFormatter.ISO_LOCAL_DATE_TIME)
                                .appendPattern("Z")
                                .toFormatter(Locale.ENGLISH);
        OffsetDateTime odt = OffsetDateTime.parse(strDateTime, dtf);
        System.out.println(odt);

        // Alternatively,
        dtf = DateTimeFormatter.ofPattern("uuuu-MM-dd'T'HH:mm:ss.SSZ", Locale.ENGLISH);
        odt = OffsetDateTime.parse(strDateTime, dtf);
        System.out.println(odt);
    }
}