After compiling Classic Java Proxy with Java 11 JDK and running using Java 11 JVM/JRE the input date format "dd/mm/yyyy" (e.g. "13/06/2023") that is accepted with the previous Java 8 version of the proxy is not able to be parsed i.e.
Exception: java.text.ParseException: Unparseable date: "13/06/2023"
The behavior occurs when using the Classic Java Proxy i.e. the Standard Java Proxy does not show the problem.
There have been some default date format changes in Java 9 and above. The Classic Java proxy uses Java class DateFormat in its generated code for the MainUI while the Standard Java proxy does not. This web page covers an example of how to restore the Java 8 behavior: Stackoverflow > SimpleDateFormat .format() gives different results in Java8 vs. Java11
It advises adding the system property "-Djava.locale.providers=COMPAT,CLDR" to the JVM command line will give the same behavior as Java 8.
It was found that running the Java 11 compiled Classic Java Proxy using Java 11 JVM with the above additional system property allowed the same date format to be parsed that was accepted with the previous Java 8 compiled proxy. In fact, the COMPAT value was enough to enable successful parsing of the date format i.e. "-Djava.locale.providers=COMPAT".
This Classic Java proxy behavior change with Java 11 is purely due to a JVM default date format change and is not actually due to a Gen specific problem.
NOTE: In general, the required date format will be specific to the Locale on the local Windows machine - see #3 in Additional Information.