不允许未登陆用户访问的过滤器配置，filter

<filter>
<filter-name>onlineFilter</filter-name>
<filter-class>filter.OnlineFilter</filter-class>
</filter>

<filter-mapping>
<filter-name>onlineFilter</filter-name>
<url-pattern>*.jsp</url-pattern>
</filter-mapping>

package filter;

import java.io.IOException;

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

public class OnlineFilter extends HttpServlet implements Filter
{
private static final long serialVersionUID = 1L;
public void init(FilterConfig filterConfig) throws ServletException
{

}
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException
{
RequestDispatcher dispatcher = request.getRequestDispatcher("KK_BlacklistVehicle_UserLogin.jsp");//这里设置如果没有登陆将要转发到的页面
HttpServletRequest req = (HttpServletRequest) request;
HttpServletResponse res = (HttpServletResponse) response;
HttpSession session = req.getSession(true);

//  System.out.println(((HttpServletRequest) request).getRequestURI());
// 从session里取的用户名信息
String username = (String) session.getAttribute("sessionKK_BlacklistVehicle_UserLogin_ID");//这里获取session，为了检查session里有没有保存用户信息，没有的话回转发到登陆页面

// 判断如果没有取到用户信息,就跳转到登陆页面
if (username == null || "".equals(username))
{
// 跳转到登陆页面
dispatcher.forward(request,response);

res.setHeader("Cache-Control","no-store");
res.setDateHeader("Expires",0);
res.setHeader("Pragma","no-cache");
}
else
{
// 已经登陆,继续此次请求
chain.doFilter(request,response);
}
}
}