过滤器

一、Filter接口
①参数
FilterConfig 类似 ServletConfig的用途
ServletRequest 请求
ServletResponse 响应
FilterChain 连接器链

②方法

public void init(FilterConfig cfg) throws ServletException public void doFilter(ServletRequest req, ServletResponse resp,            FilterChain chain) throws IOException, ServletException public void destroy()

③配置

<filter>    <filter-name>MyFilter</filter-name>    <filter-class>com.bright.filter.MyFilter</filter-class>    <init-param>        <param-name>name</param-name>        <param-value>root</param-value>    </init-param>  </filter>  <filter-mapping>    <filter-name>MyFilter</filter-name>    <url-pattern>/hello</url-pattern>  </filter-mapping><url-pattern>：  是被拦截的servlet的路径

④多个拦截器拦截同一个servlet
拦截器配置相同的url，拦截器执行的顺序，按照web.xml中配置的顺序

⑤一个拦截器拦截多个servlet
通配符匹配

⑥.使用拦截器处理字符集问题。统一处理字符集
在servlet执行之前，处理req.和resp的字符集

⑦ 非法登陆的统一处理
注意： 一定不要拦截用于登陆的servlet

⑧filter中，可以放行执行后续类，也可以直接响应浏览器

二、小项目：
1.验证码（session的使用）
2.保持用户名、密码，一周内自动登录（cookie）
3.统一设置字符集
4.非法登录的拦截器处理
5.使用session监听器，统计应用中登录的人数（通过生命周期监听器）

用户登录成功
–购物
–显示
登录失败
–显示表单重新登录
①登录表单form:FormServlet

前面导包等省略public class FormServlet extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        PrintWriter out=resp.getWriter();        out.println("用户登录<br/>");        out.println("<form action='login' method='post'>");        out.println("用户名：<input type='text' name='uname'><br/>");        out.println("<input type='checkbox' name='save' value=''>一周内自动登录<br/>");        out.println("<input type='submit' value='提交'/>");        out.println("</form>");    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        doGet(req, resp);    }   }

②处理登录login:LoginServlet

前面导包等省略public class LoginServlet extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        //先获取uname        String uname=req.getParameter("uname");        PrintWriter out=resp.getWriter();        //如果用户存在        if(uname!=null&&uname.length()>0){            HttpSession session=req.getSession();//没有session就创建            session.setAttribute("islogin", "ok");//如果登录成功，就把islogin存在session中，并记作ok            out.println("用户名："+uname+"<br/>");            out.println("恭喜你，登录成功<br/>");            out.println("<a href='user/buy'>购买</a><br/>");            out.println("<a href='user/show'>显示</a><br/>");        }else{            out.println("登录失败<br/>");            out.println("<a href='form'>重新登录</a>");        }    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        doGet(req, resp);    }}

③购物buy:BuyServlet

前面导包等省略public class BuyServlet extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {            PrintWriter out=resp.getWriter();            out.println("买买买====剁手剁手剁手");            out.flush();            out.close();    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        doGet(req, resp);    }   }

④显示信息show：ShowServlet

public class ShowServlet extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        PrintWriter out=resp.getWriter();        out.println("买好了，付款咯8888￥");        out.flush();        out.close();    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        doGet(req, resp);    }}

⑤设置字符集的过滤器：EncodingFilter

public class EncodingFilter implements Filter {    private String encoding="";    public void init(FilterConfig cfg) throws ServletException {        this.encoding=cfg.getInitParameter("encoding");    }    public void destroy() {    }    public void doFilter(ServletRequest req, ServletResponse resp,            FilterChain chain) throws IOException, ServletException {        //设置请求的字符集        req.setCharacterEncoding(encoding);        //设置响应的字符集        resp.setCharacterEncoding(encoding);        //设置响应类型        resp.setContentType("text/html");        //这一句不能少        chain.doFilter(req, resp);    }}

⑥非法登录的拦截器处理：LoginFilter

public class LoginFilter implements Filter {    public void destroy() { }    public void doFilter(ServletRequest req, ServletResponse resp,            FilterChain chain) throws IOException, ServletException {        //在请求发送之前，判断用户是否登录        HttpSession session=((HttpServletRequest)req).getSession();        //得到sesison        String islogin=(String)req.getAttribute("islogin");        //判断session是否和ok相等        if("ok".equals(islogin)){            chain.doFilter(req, resp);        }else{            ((HttpServletResponse)resp).sendRedirect("/day10/login");        }    }    public void init(FilterConfig filterConfig) throws ServletException {    }}``⑦配置：