过滤器用法案例

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07220170909

1、过滤器(Filter)：在访问servlet之前截获请求信息,同时也可以对响应信息进行拦截。中间可以定义多个Filter

2、注意注解需要这样写：@WebFilter(urlPatterns = {"/*"})//这样写表示过滤站点下所有资源

3、在使用request和response之前先向下强转[ServletRequest -> HttpServletRequest ]：

1)、HttpServletRequest req = (HttpServletRequest)request;

2)、HttpServletResponse resp = (HttpServletResponse)response;

4、chain.doFilter(req,resp);表示允许访问目标组件。

5、代码演示如下：

package com.tiger.filter;import java.io.IOException;import javax.servlet.*;import javax.servlet.annotation.WebFilter;import javax.servlet.http.*;/** * 07220170909 * 1、过滤器(Filter)：在访问servlet之前截获请求信息,同时也可以对响应信息进行拦截。中间可以定义多个Filter * 2、注意注解需要这样写：@WebFilter(urlPatterns = {"/*"})//这样写表示过滤站点下所有资源 * 3、在使用request和response之前先向下强转[ServletRequest -> HttpServletRequest ]： * 1)、HttpServletRequest req = (HttpServletRequest)request; * 2)、HttpServletResponse resp = (HttpServletResponse)response; * 4、chain.doFilter(req,resp);表示允许访问目标组件。 * @author tiger * @time 2017年9月9日 */@WebFilter("/*")public class LoginFilter implements Filter {    public LoginFilter() { }public void destroy() {System.out.println("LoginFilter.destroy()");}public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {System.out.println("MyFilter.doFilter()");HttpServletRequest req = (HttpServletRequest)request;HttpServletResponse resp = (HttpServletResponse)response;//获取请求的servlet映射路径String servlet_path = req.getServletPath();System.out.println("servlet_path = "+servlet_path);//对不是这两个资源进行过滤操作if (!"/login.html".equals(servlet_path) && !"/login".equals(servlet_path)) {String username_session = (String) req.getSession().getAttribute("username");//判断是否处于在线状态if (username_session != null) {//在线，则放行chain.doFilter(request, response);}else {//不在线则返回登陆页面resp.sendRedirect("login.html");}}else {    //提交的uri不是/login和/login.html时，则放行chain.doFilter(request, response);}}public void init(FilterConfig fConfig) throws ServletException {System.out.println("LoginFilter.init()");}}package com.tiger.servlet;import java.io.IOException;import javax.servlet.*;import javax.servlet.annotation.WebServlet;import javax.servlet.http.*;/** * 登录 * @author tiger * @time 2017年9月9日 */@WebServlet("/login")public class Login extends HttpServlet {private static final long serialVersionUID = 1L;           public Login() {  }protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {String username = request.getParameter("username");String password = request.getParameter("password");if (("tiger".equals(username) && username != null) && ("123456".equals(password) && password != null)) {request.getSession().setAttribute("username", username);System.out.println("密码正确！");}else {System.out.println("密码错误！");response.sendRedirect("login.html");}}/** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}--tiger登录页面--请输入用户名：请输入密码：

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