How to generate localized datetime from "20201023T200457Z" and from "EEE MMM dd HH:mm:ss zzz yyyy"?

Question

I have this start datetime: "20201023T200457Z" (it seem to be UTC0000) how can I convert/generate it with this "yyyyMMdd HH:mm:ss" pattern in local time on a mobile?

I get this result: Fri Oct 23 20:04:57 GMT+02:00 2020 with this code:

    SimpleDateFormat df = new SimpleDateFormat("yyyyMMdd'T'HHmmss'Z'", Locale.getDefault());
    Date startGMTInput = df.parse(start);
    Log.e(TAG, "start: " + startGMTInput.toString());// -> Fri Oct 23 20:04:57 GMT+02:00 2020

But my target is to get: 2020-10-23 22:04:57 //because I'm in GMT+2 timezone

Answer 1

Set your timezone to GMT+2 before any date operations.

isoFormat.setTimeZone(TimeZone.getTimeZone("GMT+2"));

Answer 2

java.time either through desugaring or ThreeTenABP

Consider using java.time, the modern Java date and time API, for your date and time work. Let’s first define the formatters we need:

private static final DateTimeFormatter inputFormatter
        = DateTimeFormatter.ofPattern("uuuuMMdd'T'HHmmssX");
private static final DateTimeFormatter outputFormatter
        = DateTimeFormatter.ofPattern("yyyyMMdd HH:mm:ss");

( DateTimeFormatter is thread-safe, so we can safely declare them static.) Do the time zone conversion explicitly:

    String startString = "20201023T200457Z";
    Instant start = inputFormatter.parse(startString, Instant.FROM);
    String target = start.atZone(ZoneId.systemDefault()).format(outputFormatter);
    System.out.println(target);

Output in my time zone (currently at offset +02:00 like yours):

20201023 22:04:57

Question: Doesn’t java.time require Android API level 26?

java.time works nicely on both older and newer Android devices. It just requires at least Java 6.

• In Java 8 and later and on newer Android devices (from API level 26) the modern API comes built-in. Only in this case use the method reference Instant::from instead of the constant Instant.FROM.
• In non-Android Java 6 and 7 get the ThreeTen Backport, the backport of the modern classes (ThreeTen for JSR 310; see the links at the bottom).
• On older Android either use desugaring or the Android edition of ThreeTen Backport. It’s called ThreeTenABP. In the latter case make sure you import the date and time classes from org.threeten.bp with subpackages.

Links

• Oracle tutorial: Date Time explaining how to use java.time.
• Java Specification Request (JSR) 310, where java.time was first described.
• ThreeTen Backport project, the backport of java.time to Java 6 and 7 (ThreeTen for JSR-310).
• Java 8+ APIs available through desugaring
• ThreeTenABP, Android edition of ThreeTen Backport
• Question: How to use ThreeTenABP in Android Project, with a very thorough explanation.