实现自动登录：Filter 实现思路和方式

当你勾选（记住登录状态），用cookie保存用户名和密码。不勾选，cookie失效。
所有的页面都要经过autoLoginFilter.java 的过滤器，在这类中，必须要判断cookies不为null，获得所有的cookie，得到name为user的cookie，进行用户名和密码的验证，如果不为null，则将user存入session。
在LoginServlet.java中，获得username和password参数，进行dao验证，如果不为空，放入seesion中，进行页面跳转。
创建cookie对象。setpath("/"),表示本应用下的所有路径都能访问此cookie。
对于已经正确登录的用户，再次访问其他页面必定会再次经过autoLoginFilter，这时，判断当前session中的user是否为null，不为null，直接通过。
对于**login.jsp的有关页面，不需要经过autoLoginFilter。

package com.learning.web.servlet;

import java.io.IOException;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.Cookie;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import com.learning.domain.User;

import com.learning.service.UserService;

@WebServlet("/servlet/loginServlet")

public class LoginServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

            String username = request.getParameter("username");

            String password = request.getParameter("password");

            String autologin = request.getParameter("autologin");

            UserService userService=new UserService();

            User user = userService.findUser(username, password);

            //user不为null，则登录成功

            if (user!=null) {

                //创建cookie来保存用户信息

                Cookie cookie=new Cookie("user", user.getUsername()+"&"+user.getPassword());

                cookie.setPath("/");

                //autologin不为null，则记住了登录状态

                if (autologin!=null) {

                    cookie.setMaxAge(1*60*60*24);//一天的有效时间

                }

                else {

                    cookie.setMaxAge(0);

                }

                response.addCookie(cookie);

                request.getSession().setAttribute("user", user);

                request.getRequestDispatcher("/home.jsp").forward(request, response);

            }else {

                response.sendRedirect(request.getContextPath()+"/homeLogin.jsp");

            }

    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        doGet(request, response);

    }

}

package com.learning.web.filter;

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.annotation.WebFilter;

import javax.servlet.annotation.WebInitParam;

import javax.servlet.http.Cookie;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import javax.servlet.http.HttpSession;

import javax.servlet.jsp.jstl.core.Config;

import com.learning.domain.User;

import com.learning.service.UserService;

@WebFilter(urlPatterns="/*",initParams={@WebInitParam(name="autologin",value="login"),@WebInitParam(name="",value="")})

public class AutoFilter implements Filter{

    private FilterConfig filterConfig;

    @Override

    public void destroy() {

    }

    @Override

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)

            throws IOException, ServletException {

        // 转换对象

        HttpServletRequest httpServletRequest = (HttpServletRequest) request;

        HttpServletResponse httpServletResponse = (HttpServletResponse) response;

        // 获得访问的路径

        String uri = httpServletRequest.getRequestURI();

        String contextPath = httpServletRequest.getContextPath();

        uri = uri.substring(contextPath.length() + 1);

        // 获得初始化参数

        String login = filterConfig.getInitParameter("autologin");

        System.out.println("直接通行的路径："+login);

        // 不包含"login"的路径就要进行过滤 （xxxlogin.jsp 不需要自动登录）

        if (!uri.contains(login)) {

            HttpSession session = httpServletRequest.getSession();

            User u = (User) session.getAttribute("user");

            if (u != null) {

                System.out.println("session不为null");

                chain.doFilter(request, response);

            } else {

                // 处理业务逻辑

                // 1.获得cookie 得到User的信息

                String username = "";

                String password = "";

                UserService userService = new UserService();

                Cookie[] cookies = httpServletRequest.getCookies();

                for (int i = 0;cookies!=null&& i < cookies.length; i++) {

                    if ("user".equals(cookies[i].getName())) {

                        String string = cookies[i].getValue();

                        String[] values = string.split("&");

                        username = values[0];

                        password = values[1];

                        User user = userService.findUser(username, password);

                        // 不为空则放入session

                        if (user != null) {

                            System.out.println("自动登录了");

                            httpServletRequest.getSession().setAttribute("user", user);

                        }

                    }

                }

            }

        }

        // 2.放行

        chain.doFilter(request, response);

    }

    @Override

    public void init(FilterConfig filterConfig) throws ServletException {

        this.filterConfig=filterConfig;

    }

}

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实现自动登录：Filter 实现思路和方式

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