@Override
  public void destroy() {

  }
Called by the web container to indicate to a filter that it is being
taken out of service.

<p>This method is only called once all threads within the filter's
doFilter method have exited or after a timeout period has passed.
After the web container calls this method, it will not call the
doFilter method again on this instance of the filter.

<p>This method gives the filter an opportunity to clean up any
resources that are being held (for example, memory, file handles,
threads) and make sure that any persistent state is synchronized
with the filter's current state in memory.
ambari-server/src/main/java/org/apache/ambari/server/api/UserNameOverrideFilter.java