FULL PRODUCT VERSION :
java version "9.0.4"
Java(TM) SE Runtime Environment (build 9.0.4+11)
Java HotSpot(TM) 64-Bit Server VM (build 9.0.4+11, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
Linux tichy 4.4.0-112-generic #135-Ubuntu SMP Fri Jan 19 11:48:36 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux


A DESCRIPTION OF THE PROBLEM :
Dates formatted with SimpleDateFormat under Java 8 can not be parsed back with Java 9 - the attached sources prove this to be the case with Locale GERMAN but i suspect it is valid for more than just this Locale

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
execute the attached small app under java 8  and under Java 9 - under Java9 it will break. Reasons: different results when using the same format string. The Example shows differences at the name of the day of the week and at the month of the year representations - i suspect there is more...

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Java Version 1.8.0_144
SimpleDateFormat pattern; EEE, dd MMM yyyy H:m:s
Formatted Date: Di, 20 M��r 2018 8:54:4
Parsing Java-8-formatted-date: Di, 20 M��r 2018 8:49:8
ACTUAL -
Java Version 9.0.4
SimpleDateFormat pattern; EEE, dd MMM yyyy H:m:s
Formatted Date: Di., 20 M��rz 2018 8:51:10
Parsing Java-8-formatted-date: Di, 20 M��r 2018 8:49:8
Exception in thread "main" java.text.ParseException: Unparseable date: "Di, 20 M��r 2018 8:49:8"
	at java.base/java.text.DateFormat.parse(DateFormat.java:388)
	at de.elbosso.scratch.misc.Java9DateFormatDEBug.main(Java9DateFormatDEBug.java:19)
Java Result: 1

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Exception in thread "main" java.text.ParseException: Unparseable date: "Di, 20 M��r 2018 8:49:8"
	at java.base/java.text.DateFormat.parse(DateFormat.java:388)
	at de.elbosso.scratch.misc.Java9DateFormatDEBug.main(Java9DateFormatDEBug.java:19)

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.io.IOException;
import java.text.ParseException;

public class Java9DateFormatDEBug
{
	public static void main(String[] args) throws IOException, ParseException
	{
		java.lang.String pattern="EEE, dd MMM yyyy H:m:s";
		java.text.DateFormat rssf = new java.text.SimpleDateFormat(
				pattern, java.util.Locale.GERMAN);
		System.out.println("Java Version "+System.getProperty("java.version"));
		System.out.println("SimpleDateFormat pattern; "+pattern);
		java.util.Calendar cal = java.util.Calendar.getInstance();
		cal.set(cal.MONTH, 2);
		System.out.println("Formatted Date: "+rssf.format(cal.getTime()));
		System.out.println("Parsing Java-8-formatted-date: Di, 20 M��r 2018 8:49:8");
		rssf.parse("Di, 20 M��r 2018 8:49:8");
	}
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
There is none as far as i can see