深入理解Java中Filter的作用种类及应用场景

public class MyFilter implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {
        // 初始化操作
    }
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        // 过滤器逻辑处理
        chain.doFilter(request, response);
    }
    public void destroy() {
        // 销毁操作
    }
}

<filter>
    <filter-name>MyFilter</filter-name>
    <filter-class>com.example.MyFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>MyFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

<filter>
    <filter-name>FilterA</filter-name>
    <filter-class>com.example.FilterA</filter-class>
</filter>
<filter-mapping>
    <filter-name>FilterA</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>
<filter>
    <filter-name>FilterB</filter-name>
    <filter-class>com.example.FilterB</filter-class>
</filter>
<filter-mapping>
    <filter-name>FilterB</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 获取用户名和密码
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        // 验证用户名和密码
        if ("admin".equals(username) && "123456".equals(password)) {
            // 登录成功，保存用户信息到Session中
            HttpSession session = request.getSession();
            session.setAttribute("username", username);
            // 保存自动登录信息到Cookie中
            Cookie cookie = new Cookie("autologin", username + ":" + password);
            cookie.setMaxAge(7 * 24 * 60 * 60); // 设置Cookie过期时间为一周
            response.addCookie(cookie);
            // 跳转到首页
            response.sendRedirect(request.getContextPath() + "/index.jsp");
        } else {
            // 登录失败，返回登录页面
            response.sendRedirect(request.getContextPath() + "/login.jsp");
        }
    }
}

public class AutoLoginFilter implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {
        // 初始化操作
    }
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        // 判断用户是否已经登录
        HttpSession session = ((HttpServletRequest) request).getSession();
        String username = (String) session.getAttribute("username");
        if (username == null) {
            // 判断是否存在Cookie
            Cookie[] cookies = ((HttpServletRequest) request).getCookies();
            if (cookies != null) {
                for (Cookie cookie : cookies) {
                    if ("autologin".equals(cookie.getName())) {
                        // 自动填充用户名和密码
                        String[] values = cookie.getValue().split(":");
                        String autologinUsername = values[0];
                        String autologinPassword = values[1];
                        request.setAttribute("autologinUsername", autologinUsername);
                        request.setAttribute("autologinPassword", autologinPassword);
                    }
                }
            }
        }
        chain.doFilter(request, response);
    }
    public void destroy() {
        // 销毁操作
    }
}

public class UserServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 获取表单数据
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        int age = Integer.parseInt(request.getParameter("age"));
        // 将数据封装成User对象
        User user = new User();
        try {
            BeanUtils.setProperty(user, "username", username);
            BeanUtils.setProperty(user, "password", password);
            BeanUtils.setProperty(user, "age", age);
        } catch (Exception e) {
            e.printStackTrace();
        }
        // 保存用户信息
        UserService userService = new UserService();
        userService.saveUser(user);
        // 跳转到用户列表页面
        response.sendRedirect(request.getContextPath() + "/user/list.jsp");
    }
}