Java SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'") gives timezone as IST

java

date-formatting

timezone-management

java-date-api

byAlex Kataev·Jan 3, 2025

Your SimpleDateFormat object is confusing 'Z' for your local timezone (such as IST), and it should be UTC. Instead, implement UTC like this:

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'");
sdf.setTimeZone(TimeZone.getTimeZone("UTC"));  // like telling a dog: "sit!", and it sits.

To confidently handle this in modern versions of Java, use the java.time package:

Instant now = Instant.parse("2023-01-01T15:30:00Z"); // She loves me, she loves me 'Z' :)

For accurate UTC management, TimeZone.getTimeZone("UTC") and Instant.parse(), never fail.

Understanding `'Z'` vs `TimeZone`

The date and time pattern "yyyy-MM-dd'T'HH:mm:ss'Z'" is ideally crafted to represent a UTC timestamp. However, the role 'Z' plays here can be deceiving. It seems to direct you towards the Zulu time zone (essentially UTC), but without properly setting the timezone, SimpleDateFormat will resort to the system's timezone by default.

So in reality, employing 'Z' barely changes the timezone. It's crucial to set the TimeZone for your SimpleDateFormat object in a manner like this:

sdf.setTimeZone(TimeZone.getTimeZone("GMT")); // now performing the 'GMT shuffle'

Accommodating various time zones

'X' for flexible time zone handling

When handling ISO 8601 time zones, you can use 'X' at the end of the pattern for flexible adaptation:

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssX");
Date date = sdf.parse("2023-01-01T15:30:00Z"); // Slide smoothly into UTC

Using `java.time` for modern Java

The java.time package is designed to cater to ISO 8601 in a broader and more intuitive manner:

ZonedDateTime zdt = ZonedDateTime.parse("2023-01-01T15:30:00Z");
ZoneId zoneId = ZoneId.of("Asia/Kolkata");
ZonedDateTime zdtInKolkata = zdt.withZoneSameInstant(zoneId); // Welcome to Kolkata!

The conversion between time zones

You can convert a UTC Instant to a different time zone with atZone:

Instant.now().atZone(ZoneId.of("Asia/Kolkata")); // Let's switch the scene

📌 Key Tip: java.time is always a better choice in modern Java development. If SimpleDateFormat is your only option, never forget to set the time zone explicitly.

Overcoming complications

Remember to tackle the following issues while dealing with time zones:

Inconsistent Behaviour: Always test your software thoroughly as different JDK versions may display different behaviours towards timezone management.
Confusing Patterns: Patterns like "yyyy-MM-dd'T'HH:mm:ss'Z'" can be misleading. Using 'X' for the time zone parsing or switching to java.time is safer.
The Old API: TimeZone and SimpleDateFormat belong to the older Java Date API and can be less intuitive and often lead to errors.