How to convert HH:mm:ss.SSS to milliseconds?

问题:

I have a String 00:01:30.500 which is equivalent to 90500 milliseconds. I tried using SimpleDateFormat which give milliseconds including current date. I just need that String representation to milliseconds. Do I have to write custom method, which will split and calculate milliseconds? or Is there any other way to do this? Thanks.

I have tried as follows:

        String startAfter = "00:01:30.555";
        SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss.SSS");
        Date date = dateFormat.parse(startAfter);
        System.out.println(date.getTime());

回答1:

You can use SimpleDateFormat to do it. You just have to know 2 things.

1. All dates are internally represented in UTC
2. .getTime() returns the number of milliseconds since 1970-01-01 00:00:00 UTC.

package se.wederbrand.milliseconds;

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;

public class Main {        
    public static void main(String[] args) throws Exception {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");
        sdf.setTimeZone(TimeZone.getTimeZone("UTC"));

        String inputString = "00:01:30.500";

        Date date = sdf.parse("1970-01-01 " + inputString);
        System.out.println("in milliseconds: " + date.getTime());        
    }
}

回答2:

If you want to parse the format yourself you could do it easily with a regex such as

private static Pattern pattern = Pattern.compile("(\\d{2}):(\\d{2}):(\\d{2}).(\\d{3})");

public static long dateParseRegExp(String period) {
    Matcher matcher = pattern.matcher(period);
    if (matcher.matches()) {
        return Long.parseLong(matcher.group(1)) * 3600000L 
            + Long.parseLong(matcher.group(2)) * 60000 
            + Long.parseLong(matcher.group(3)) * 1000 
            + Long.parseLong(matcher.group(4)); 
    } else {
        throw new IllegalArgumentException("Invalid format " + period);
    }
}

However, this parsing is quite lenient and would accept 99:99:99.999 and just let the values overflow. This could be a drawback or a feature.

回答3:

If you want to use SimpleDateFormat, you could write:

private final SimpleDateFormat sdf =
    new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");
    { sdf.setTimeZone(TimeZone.getTimeZone("GMT")); }

private long parseTimeToMillis(final String time) throws ParseException
    { return sdf.parse("1970-01-01 " + time).getTime(); }

But a custom method would be much more efficient. SimpleDateFormat, because of all its calendar support, time-zone support, daylight-savings-time support, and so on, is pretty slow. The slowness is worth it if you actually need some of those features, but since you don't, it might not be. (It depends how often you're calling this method, and whether efficiency is a concern for your application.)

Also, SimpleDateFormat is non-thread-safe, which is sometimes a pain. (Without knowing anything about your application, I can't guess whether that matters.)

Personally, I'd probably write a custom method.

回答4:

Using JODA:

PeriodFormatter periodFormat = new PeriodFormatterBuilder()
  .minimumParsedDigits(2)
  .appendHour() // 2 digits minimum
  .appendSeparator(":")
  .minimumParsedDigits(2)
  .appendMinute() // 2 digits minimum
  .appendSeparator(":")
  .minimumParsedDigits(2)
  .appendSecond()
  .appendSeparator(".")
  .appendMillis3Digit()
  .toFormatter();
Period result = Period.parse(string, periodFormat);
return result.toStandardDuration().getMillis();