@Override
  public void init(FilterConfig filterConfig) throws ServletException {

  }
Called by the web container to indicate to a filter that it is
being placed into service.

<p>The servlet container calls the init
method exactly once after instantiating the filter. The init
method must complete successfully before the filter is asked to do any
filtering work.

<p>The web container cannot place the filter into service if the init
method either
<ol>
<li>Throws a ServletException
<li>Does not return within a time period defined by the web container
</ol>

@param filterConfig
ambari-server/src/main/java/org/apache/ambari/server/api/UserNameOverrideFilter.java