java web过滤器之用户登录过滤

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package cn.itcast.filters;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class UserAccessFilter implements Filter {

public void doFilter(ServletRequest req, ServletResponse res,
   FilterChain chain) throws IOException, ServletException {
  HttpServletRequest request = (HttpServletRequest) req;
  HttpServletResponse response = (HttpServletResponse) res;

  StringBuffer sb = request.getRequestURL();
  String url = sb.toString();
  HttpSession session = request.getSession(false);
  if (url.contains("/LoginServlet")||url.contains("/ToLoginJspServlet")||url.contains("/login.jsp")) {
   chain.doFilter(request, response);
  } else {
   if (session != null) {
    Object o = session.getAttribute("UserInfo");
    if (o != null) {
     chain.doFilter(request, response);
    } else {
     response.sendRedirect("ToLoginJspServlet");
    }

   } else {
    response.sendRedirect("ToLoginJspServlet");
   }

}
}

public void init(FilterConfig arg0) throws ServletException {

}

public void destroy() {

}

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