import java.time.Instant;
import java.time.OffsetDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Locale;
 
public class Main {
	public static void main(String[] args) {
		String strDateTime = "2021010112:12:12.10:00";
		strDateTime = strDateTime.replaceFirst("\\.(\\d{1,2}:\\d{1,2})", ".+$1");
 
		DateTimeFormatter dtf = DateTimeFormatter.ofPattern("uuuuMMddHH:mm:ss.XXX", Locale.ENGLISH);
		Instant instant = OffsetDateTime.parse(strDateTime, dtf).toInstant();
		System.out.println(instant);
	}
}

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