package liuxiaobo.filter;import javax.servlet.*;import javax.servlet.http.*;import java.io.*;public class SessionAuthorizationFilter implements Filter {  protected FilterConfig filterConfig;  public void init(FilterConfig config) {    this.filterConfig = config;  }  public void destroy() {    this.filterConfig = null;  }  private boolean passed(ServletRequest request, ServletResponse response)      throws IOException, ServletException {    boolean result=false;    String objectName=this.filterConfig.getInitParameter("OBJECT_NAME");    HttpServletRequest req = (HttpServletRequest)request;    HttpSession session =req.getSession(false);    if(session!=null){      Object object=session.getAttribute(objectName);      if(object!=null)        result= true;    }      return result;  }  public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)      throws IOException, ServletException{    if (passed(request,response))        filterChain.doFilter(request, response);    else{      HttpServletResponse res = (HttpServletResponse)response;      String errorPage=this.filterConfig.getInitParameter("ERROR_PAGE");      res.sendRedirect(errorPage);    }  }}