[初学]过滤器的使用

 

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;//二.过滤器的使用：public class LoginFilter implements Filter {public void destroy() {}public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {HttpServletRequest httpRequest = (HttpServletRequest) request;HttpServletResponse httpResponse = (HttpServletResponse) response;HttpSession session = httpRequest.getSession();User userBean = (User) session.getAttribute("user");if (userBean == null) {// 当没有Session时 跳转到登陆页面httpResponse.sendRedirect(httpRequest.getContextPath() + "/index.jsp");} else {chain.doFilter(request, response);}}public void init(FilterConfig arg0) throws ServletException {}/* * web.xml中配置(过滤WebRoot目录下的back文件夹下的所有jsp文件)：  * <filter> * <filter-name>loginFilter</filter-name> * <filter-class>com.jungle.filter.LoginFilter</filter-class> * </filter> *  * <filter-mapping> * <filter-name>loginFilter</filter-name> * <url-pattern>/back/*</url-pattern> * </filter-mapping> */}class User {}