在Struts2中编写过滤器需要创建一个类，继承 import javax.servlet.Filter; 下面，创建一个判断用户是否登录的Filter：
public class UserLoginValidateFilter implements Filter {
@Override
public void destroy() {
}
@Override
public void doFilter(ServletRequest req, ServletResponse res,
FilterChain filterChain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest)req;
User user = WebUtil.getUser(request);
if(user == null){
HttpServletResponse response = (HttpServletResponse)res;
response.sendRedirect(request.getContextPath() + "/user/Login.action");
}else{
filterChain.doFilter(req, res);
}
}
@Override
public void init(FilterConfig arg0) throws ServletException {
}
}
接下来在web.xml文件中注册，设置需要过滤的URL：
