How to access PortalRequestContext object in EPP

Issue

• How to access the PortalRequestContext from a FilterServlet and from a HTTPServlet. For instance, if a customer is interested in fetching the siteName.

• Error when trying to access PortalRequestContext to fetch the siteName.

WARN  [SetCurrentIdentityFilter] An error occured while cache user profile
java.lang.NullPointerException
    at org.exoplatform.portal.webui.util.Util.getPortalRequestContext(Util.java:53)
    at filters.TestFilter.doFilter(TestFilter.java:43)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)

Code snippet used to fetch is similar to -

    PortalRequestContext context = Util.getPortalRequestContext();
//  String remUser = context.getRemoteUser();
//        String siteName = context.getSiteName();
//   System.out.println("Site Name is:" +siteName);
    String requestParam = context.getRequestParameter("requestParameter");

and the entry in web.xml has

 <filter>
           <filter-name>TestFilter</filter-name>
           <filter-class>filters.TestFilter</filter-class>
      </filter>
      <filter-mapping>
           <filter-name>TestFilter</filter-name>
           <url-pattern>/abc</url-pattern>
      </filter-mapping>