将UTC日期从科学记数法转换为Java.util.Date

Question

I'm trying to convert the created_utc date from Reddit's json to a Date object, but I keep getting an "Unparceable" error. An example of their dates is: created_utc": 1.43701862E9, which I'm told is a unix timestamp.

From my research this code should convert it:

String date = "1.43701862E9";
java.util.Date time = new java.util.Date((long)date*1000);

but obviously I'm getting an error on multiplying the date by 1000.

This is the code I normally use to convert string dates:

    String date = "1.43701862E9";
    Calendar cal = Calendar.getInstance(TimeZone.getDefault());
    SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss z");
    format.parse(date);

Answer 1

This should work for you:

public static void main(String[] args) {

    String date = "1.43701862E9";
    java.util.Date time = new java.util.Date(Double.valueOf(date).longValue()*1000);

    System.out.println(time);
}

Output:

Wed Jul 15 23:50:20 EDT 2015

---

Since you're using scientific notation you can't parse the String using the Long class: Long.parseLong(String s) (Nor can you simply cast a String, as you're trying). Instead, I used the Double.valueOf() method and preserve the Long using .longValue()

Answer 2

The answer by Trobbins is correct but old-school. I lifted that Answer's math, and used the new java.time classes.

java.time

In Java 8 and later, you can use the new java.time package which supplants the troublesome old java.util.Date /.Calendar classes. ( Tutorial )

String input = "1.43701862E9";
long milliSinceEpoch = Double.valueOf( input ).longValue() * 1_000L ;
Instant instant = Instant.ofEpochMilli( milliSinceEpoch ) ;
ZoneId zoneId = ZoneId.of( "America/Montreal" ) ;
ZonedDateTime zdt = ZonedDateTime.ofInstant( instant , zoneId ) ;

Try to avoid java.util.Date/.Calendar, but if need be you can convert.

java.util.Date date = Date.from( zdt.toInstant() );  // Or… Date.from( instant );
java.util.Calendar calendar = GregorianCalendar.from( zdt );