How to parse a ISO 8601 to Date in Java?

Question

I'm trying to parse a ISO 8601 date to a Date object, but I can't.

I'm trying the following:

        String date = "2021-05-14T09:26:20";
        
        SimpleDateFormat parser = new SimpleDateFormat("yyyy-MM-dd HH:MM:ss");
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:MM:ss");
        Date newDate = parser.parse(date);
        System.out.println(format.format(newDate));

But I get this error:

Exception in thread "main" java.text.ParseException: Unparseable date: "2021-05-14T09:26:20"
    at java.text.DateFormat.parse(DateFormat.java:366)
    at com.pruebas.pruebas.fechas.main(fechas.java:14)

How can I solve this?

Answer 1

Problems with your code:

1. The pattern for parsing should match with the given date-time string. You have missed 'T' in the pattern for parsing.
2. Also, you have used M instead of m for "Minute in hour". The symbol, M is used for "Month in year". Read the documentation carefully.

Demo with correct patterns:

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class Main {
    public static void main(String[] args) throws ParseException {
        String date = "2021-05-14T09:26:20";
        SimpleDateFormat parser = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date newDate = parser.parse(date);
        System.out.println(format.format(newDate));
    }
}

ONLINE DEMO

Introducing java.time, the modern Date-Time API:

Note that the java.util Date-Time API and their formatting API, SimpleDateFormat are outdated and error-prone. It is recommended to stop using them completely and switch to the modern Date-Time API^*, released in March 2014 as part of Java SE 8 standard library.

Solution using java.time, the modern Date-Time API:

The modern Date-Time API is based on ISO 8601 and does not require using a DateTimeFormatter object explicitly as long as the Date-Time string conforms to the ISO 8601 standards.

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Locale;

public class Main {
    public static void main(String[] args) {
        String date = "2021-05-14T09:26:20";
        LocalDateTime ldt = LocalDateTime.parse(date);
        System.out.println(ldt);
        
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("uuuu-MM-dd HH:mm:ss", Locale.ENGLISH);
        System.out.println(dtf.format(ldt));
    }
}

Output:

2021-05-14T09:26:20
2023-02-14 09:02:20

ONLINE DEMO

Here, you can use y instead of u but I prefer u to y.

Learn more about the modern Date-Time API from Trail: Date Time.

---

^{* For any reason, if you have to stick to Java 6 or Java 7, you can use ThreeTen-Backport which backports most of the java.time functionality to Java 6 & 7. If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8+ APIs available through desugaring and How to use ThreeTenABP in Android Project.}

Answer 2

Though @Arvind gave some good explanations and examples your issue in this particular instance is simply a typo. The string:

String date = "2021-05-14T09:26:20";

includes a T literal to separate the date from the time as per the ISO-8601 standard. You have simply forgotten this in your SimpleDateFormat:

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

You should have this:

SimpleDateFormat parser = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");

And all should work.