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Hi want to convert UTC times to local time and i am doing this

public class TimeZoneN 
 public static void main( String args ) throws ParseException 

 String timeStr1 = "2018-11-08_21h34m46sZ";

 String formatStr1 = "yyyy-MM-dd_HH'h'mm'm'ss's'Z";

 SimpleDateFormat formatter = new SimpleDateFormat( formatStr1 );
 formatter.setTimeZone( TimeZone.getTimeZone( "UTC" ) );

 Date date1 = formatter.parse( timeStr1 );
 System.out.println( date1 );

 

i am getting a parse exception because od the Z, but when i do

String formatStr1 = "yyyy-MM-dd_HH'h'mm'm'ss'sZ'";

It passes, is that valid though ? Woudn't that consider sZ as a single constant and not Z as the timezone token ?

You are correct that Z denotes Zulu time, another name for UTC. You may also think of it as offset zero from UTC. So you will want to parse Z as an offset to ensure that your time is interpreted correctly.

java.time

However, don’t use SimpleDateFormat. It’s notoriously troublesome and long outdated. Don’t use Date either, it too is long outdated and it too has design problems.

 DateTimeFormatter formatter
 = DateTimeFormatter.ofPattern("uuuu-MM-dd_H'h'm'm's's'X");
 String timeStr1 = "2018-11-08_21h34m46sZ";
 Instant instant1 = formatter.parse(timeStr1, Instant::from);
 System.out.println(instant1);

Output:

2018-11-08T21:34:46Z

For the sake of completeness:

want to convert … to local time

Taking America/Toronto as a random example:

 ZonedDateTime dateTime = instant1.atZone(ZoneId.of("America/Toronto"));
 System.out.println(dateTime);

Output:

2018-11-08T16:34:46-05:00[America/Toronto]

In a comment you asked about Z:

what difference would that make if i dont include it at all ?

Two things:

• You want to make sure the string includes the required offset and object if not, or you risk that errors pass unnoticed. It’s called input validation.


• As I mentioned you want to parse Z as an offset or you cannot extract an unambiguous point in time from the parsed values.

Link: Oracle tutorial: Date Time explaining how to use java.time.