Java SimpleDateFormat throwing ParseException: Unparseable date on Windows but not on Mac

erik p :

I have the following method:

    public static Date convertFromWowInterface(String wowinterfaceFormat){
        Date date = null;
        try {
            SimpleDateFormat dateFormat = new SimpleDateFormat("MM-dd-yy hh:mm a");
            date = dateFormat.parse(wowinterfaceFormat);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return date;
    }

The string being passed in is of the format:

"08-11-19 07:00 AM"

without the quotes obviously. Now the above method works just fine on my mac, however when some of my users use the program (on Windows) they get the exception:

java.text.ParseException: Unparseable date: "08-11-19 07:00 AM"
        at java.base/java.text.DateFormat.parse(DateFormat.java:395)

Does the OS make a difference here? Or is there something else at play? As far as I can tell the SimpleDateFormat match the input string exactly?

Robert :

I can reproduce the problem when I switch to a different locale.

Here's my demo program:

import java.util.*;
import java.text.*;

public class YourCode {
    public static void main(String[] args) throws Exception {
        for (String a : args) {
            SimpleDateFormat dateFormat = new SimpleDateFormat("MM-dd-yy hh:mm a");
            Date d = dateFormat.parse(a);
            System.out.println(d);
        }
    }
}

It works, when I run it under US English locale:

robert@saaz:~$ LC_ALL="en_US.UTF-8" java YourCode "08-11-19 07:00 AM" 
Sun Aug 11 07:00:00 CDT 2019

I get the exception you see when I switch to e.g., German locale, which uses 24h time, not AM/PM.

robert@saaz:~$ LC_ALL="de_DE.UTF-8" java YourCode "08-11-19 07:00 AM" 
Exception in thread "main" java.text.ParseException: Unparseable date: "08-11-19 07:00 AM"
    at java.base/java.text.DateFormat.parse(DateFormat.java:395)
    at YourCode.main(YourCode.java:8)

To get around this, specify the locale when you create the SimpleDateFormat. Change

SimpleDateFormat dateFormat = new SimpleDateFormat("MM-dd-yy hh:mm a");

to

SimpleDateFormat dateFormat = new SimpleDateFormat("MM-dd-yy hh:mm a", Locale.US);