Using filters in Java

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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();        }           }