Unix epoch time to Java Date object

问题:

I have a string containing the UNIX Epoch time, and I need to convert it to a Java Date object.

String date = \"1081157732\";
DateFormat df = new SimpleDateFormat(\"\"); // This line
try {
  Date expiry = df.parse(date);
 } catch (ParseException ex) {
  ex.getStackTrace();
}

The marked line is where I\'m having trouble. I can\'t work out what the argument to SimpleDateFormat() should be, or even if I should be using SimpleDateFormat().

回答1:

How about just:

Date expiry = new Date(Long.parseLong(date));

EDIT: as per rde6173\'s answer and taking a closer look at the input specified in the question , \"1081157732\" appears to be a seconds-based epoch value so you\'d want to multiply the long from parseLong() by 1000 to convert to milliseconds, which is what Java\'s Date constructor uses, so:

Date expiry = new Date(Long.parseLong(date) * 1000);

回答2:

Epoch is the number of seconds since Jan 1, 1970..

So:

String epochString = \"1081157732\";
long epoch = Long.parseLong( epochString );
Date expiry = new Date( epoch * 1000 );

For more information: http://www.epochconverter.com/

回答3:

java.time

Using the java.time framework built into Java 8 and later.

import java.time.LocalDateTime;
import java.time.Instant;
import java.time.ZoneId;

long epoch = Long.parseLong(\"1081157732\");
Instant instant = Instant.ofEpochSecond(epoch);
ZonedDateTime.ofInstant(instant, ZoneOffset.UTC); # ZonedDateTime = 2004-04-05T09:35:32Z[UTC]

In this case you should better use ZonedDateTime to mark it as date in UTC time zone because Epoch is defined in UTC in Unix time used by Java.

ZoneOffset contains a handy constant for the UTC time zone, as seen in last line above. Its superclass, ZoneId can be used to adjust into other time zones.

ZoneId zoneId = ZoneId.of( \"America/Montreal\" );

回答4:

long timestamp = Long.parseLong(date)
Date expiry = new Date(timestamp * 1000)

回答5:

Better yet, use JodaTime. Much easier to parse strings and into strings. Is thread safe as well. Worth the time it will take you to implement it.

回答6:

To convert seconds time stamp to millisecond time stamp. You could use the TimeUnit API and neat like this.

long milliSecondTimeStamp = MILLISECONDS.convert(secondsTimeStamp, SECONDS)

回答7:

Hum.... if I am not mistaken, the UNIX Epoch time is actually the same thing as

System.currentTimeMillis()

So writing

try {
    Date expiry = new Date(Long.parseLong(date));
}
catch(NumberFormatException e) {
    // ...
}

should work (and be much faster that date parsing)