Using filters in Java

public void doFilter(ServletRequest req,ServletResponse resp,FilterChain chain){
    try{
 HttpSession session = ((HttpServletRequest)req).getSession(false);
 if(session!=null){
            String userName = (String) session.getAttribute("userid");
            if(userName==null || userName.equals("")){
                   //Invalid user. Redirect to login page
 String message= "You have been logged out of the application. Please log in again.";
  session.setAttribute("message", message);
  ((HttpServletResponse)resp).sendRedirect(((HttpServletRequest)req).getContextPath()+session.getServletContext().getInitParameter("initPage"));
  }
  else{
                                                //If valid user, forward the request
   chain.doFilter(req, resp); 
  }
 }
 else{
  ((HttpServletResponse)resp).sendRedirect("errorPage.html");  }
 }
catch(ServletException se){
  System.out.println("In Servlet Exception");
  try{
   throw se.getRootCause();
  }
  catch(Throwable e){
   e.printStackTrace();
  }
   se.printStackTrace();
   
  }
  catch(IOException ioe){
   System.out.println("In IO Exception");
   ioe.printStackTrace();
   
  }
  
   
 }