java.lang.IllegalArgumentException: Bad class: class java.util.GregorianCalendar

A Calendar can't be directly formatted, you need to get the Date from the Calendar, like this:

String formattedDate = dateFormat.format(someDate.getTime());

As one of the answers here: Using GregorianCalendar with SimpleDateFormat says "A SimpleDateFormat, as its name indicates, formats Dates."

So, try this:

String formattedDate = dateFormat.format(someDate.getDate());

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