How to convert timestamp into date and time in java?

Question

I have a timestamp in json that is from a Linux server. I would like to convert it into a simple date-time format using Java.

I need the date and time in the following format: dd-mm-yyyy hh:mm:ss

here is my JSON data:

[
  { 
    "batch_date": 1419038000
  }, 
  {
    "batch_date": 1419037000
  }
]

Answer 1

The batch date

"batch_date": 1419038000, 

looks like seconds from epoch,

so

new Date (batch_date * 1000); 

then use SimpleDateFormat should do the trick

SimpleDateFormat sfd = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");

-- code --

    long batch_date = 1419038000; 
    Date dt = new Date (batch_date * 1000); 

    SimpleDateFormat sfd = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");
    System.out.println(sfd.format(dt));

-- output --

20-12-2014 10:13:20

Answer 2

No Such Data Type

There is no such thing as "JSON timestamp". JSON has very few defined data types . No date-time types among them.

As the correct Answer by Scary Wombat states, your number is apparently a count of whole seconds from the Unix epoch of 1970. The java.util.Date class tracks time as milliseconds since the Unix epoch , rather than whole seconds. So you need to multiply by 1,000. You also need to deal with long integers (64-bit) rather than int (32-bit). Append an uppercase L to the numeric literals, and declare any variables as long .

The java.util.Date/.Calendar classes are notoriously troublesome. They are now supplanted by the java.time package built into Java 8 and later, and/or the 3rd-party Joda-Time library.

Various JSON-processing libraries support converters for creating java.time or Joda-Time objects. Or you can perform a conversion in your code, shown below.

Be aware that both java.time and Joda-Time supports assigning a time zone. Code below assigns UTC for demonstration purposes, but you can assign your desired/expected zone.

Joda-Time

Here is some code in Joda-Time 2.8.1 showing the use of your input number as either seconds or milliseconds.

long secondsSinceEpoch = 1419038000L;
DateTime dateTimeSeconds = new DateTime( secondsSinceEpoch , DateTimeZone.UTC );
DateTime dateTimeMillis = new DateTime( secondsSinceEpoch * 1000L , DateTimeZone.UTC );  // Note the crucial "L" appended to the numeric literal.

Dump to console.

System.out.println( "dateTimeSeconds: " + dateTimeSeconds );
System.out.println( "dateTimeMillis: " + dateTimeMillis );

When run.

dateTimeSeconds: 1970-01-17T10:10:38.000Z
dateTimeMillis: 2014-12-20T01:13:20.000Z

java.time

Similar code to above, but using java.time of Java 8.

Instant instant = Instant.ofEpochSecond( 1419038000L );
ZonedDateTime zdtUtc = ZonedDateTime.ofInstant( instant , ZoneOffset.UTC );
ZonedDateTime zdtMontréal = zdtUtc.withZoneSameInstant( ZoneId.of( "America/Montreal" ) );

Dump to console.

System.out.println( "zdtUtc: " + zdtUtc );
System.out.println( "zdtMontréal: " + zdtMontréal );

When run.

zdtUtc: 2014-12-20T01:13:20Z
zdtMontréal: 2014-12-19T20:13:20-05:00[America/Montreal]

Answer 3

when we want read/parse a string value as date, we should know the date format of that input string, otherwise we will get wrong date value.

batch_date:1419038000 what is the date format of this value ?

If we want to get the date value in the required format as in your case 'dd-mm-yyyy hh:mm:ss'. there are two possible ways.

1) request batch_date value should be in your required format. or

2) if batch_date value is another format, we should know the original format, and build a Date object with original format using SimpleDateFormat parse method and then convert it into required format using another SimpleDateFormat format method.