title: Sorting a map on key of type XMLGregorianCalendar
body: <p>I have a <code>Map&lt;XMLGregorianCalender,Long&gt;</code>. I want to sort the data by <code>DESCENDING XMLGregorianCalender</code> and put the data into another <code>TreeMap</code>. </p>
  
  <p>I tried overriding implementing <code>Comparator</code> method, but failed.
  Can anybody help? </p>