监听器(自动登录)

1.filter概述

可以过滤从客户端向服务器发送的请求
进行IP的过滤,脏话过滤,自动登录
编写一个类实现Filter接口;

2.filter的生命周期

创建:服务器启动的时候.
销毁:服务器关闭的时候.

3.FilterConfig:过滤器的配置对象

public void init(FilterConfig filterConfig) throws ServletException {
        // 获得当前的Filter的名称:
        String filterName = filterConfig.getFilterName();
        System.out.println(filterName);
        // 获得初始化参数:
        String username = filterConfig.getInitParameter("username");
        String password = filterConfig.getInitParameter("password");
        System.out.println(username+"   "+password);
        // 获得所有的初始化参数的名称:
        Enumeration<String> en = filterConfig.getInitParameterNames();
        while(en.hasMoreElements()){
            String name = en.nextElement();
            String value = filterConfig.getInitParameter(name);
            System.out.println(name+"    "+value);
        }
    }

4.FilterChain:过滤器链

过滤器链中的过滤器的执行的顺序与<filter-mapping>的配置顺序有关.
doFilter(request,response); -- 放行,放行到下一个过滤器中,如果没有下一个过滤器,到达目标资源.

5.Filter相关的配置

? <url-pattern>的配置：
* 完全路径匹配 ：以 / 开始 /demo4/demo1.jsp
* 目录匹配 ：以 / 开始 以 * 结束. /* /demo1/*
* 扩展名匹配 ：不能以 / 开始 以 * 开始. *.do *.action

? <servlet-name>的配置:根据Servlet的名称拦截Servlet.

? <dispatcher>的配置:
* REQUEST :默认值.
* FORWARD :转发.
* INCLUDE :包含.
* ERROR :错误页面跳转.(全局错误页面)

6.自动登录的案例

/**
 * 这是一个登录的servlet
 * 这个案例没有做中文的处理
 * 
 */
public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        try {
            //获取表单数据
            User user = new User();
            BeanUtils.populate(user, request.getParameterMap());
            UserService us = new UserService();
            User users = us.login(user);
            
            if(users != null) {
                //判断是否勾选自动登录
                String autoLogin = request.getParameter("autoLogin");
                if(autoLogin != null) {
                    Cookie password_cookie = new Cookie("password_cookie", users.getPassword());
                    Cookie username_cookie = new Cookie("username_cookie", users.getUsername());
                    
                    password_cookie.setMaxAge(30*60);
                    
                    username_cookie.setMaxAge(30*60);
                    
                    //发送cookie出去
                    response.addCookie(username_cookie);
                    response.addCookie(password_cookie);
                    //在过滤器中检测cookie
                }
                request.setAttribute("user", users);
                request.getRequestDispatcher("/index.jsp").forward(request, response);
            }else {
                String loginInfo = "用户名或密码错误";
                request.setAttribute("loginInfo", loginInfo);
                request.getRequestDispatcher("/login.jsp").forward(request, response);
                
            }
        } catch (Exception e) {
            e.printStackTrace();
        } 
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

/**
 * 这是一个自动登录的过滤器
 * */
public class AutoLoginFilter implements Filter{

    @Override
    public void destroy() {
        
    }

    @Override
    public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)
            throws IOException, ServletException {
        System.out.println("AutoLoginFilter");
        //获得request和response
        HttpServletRequest request = (HttpServletRequest) arg0;
        HttpServletResponse response = (HttpServletResponse) arg1;
        //获得所有cookie
        Cookie[] cookies = request.getCookies();
        //调用cookie的工具类
        Cookie username_cookie = CookieUtils.findCookie(cookies, "username_cookie");
        Cookie password_cookie = CookieUtils.findCookie(cookies, "password_cookie");
        
        User user = new User();
        if(username_cookie != null && password_cookie != null) {
            //取出存在特定cookie中的用户名和密码
            String username = username_cookie.getValue();
            String password = password_cookie.getValue();
            //设置到user对象中
            user.setUsername(username);
            user.setPassword(password);
            //创建session对象
            HttpSession session = request.getSession();
            UserDao ud = new UserDao();
            User users = null;
            try {
                //调用dao层判断cookie有没有发生变化
                users = ud.login(user);
                //保存到session域
                session.setAttribute("user", users);
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        //放行
        arg2.doFilter(request, response);
    }

    @Override
    public void init(FilterConfig arg0) throws ServletException {
        
    }
    
}

cookie工具类:

/**
 * Cookie的工具类
 * @author admin
 *
 */
public class CookieUtils {

    public static Cookie findCookie(Cookie[] cookies,String name){
        if(cookies == null){
            return null;
        }else{
            for(Cookie cookie:cookies){
                if(name.equals(cookie.getName())){
                    return cookie;
                }
            }
            
            return null;
        }
    }
}

7.解决中文乱码问题

public class MyHttpServletRequestWrapper extends HttpServletRequestWrapper{

    private HttpServletRequest request;

    public MyHttpServletRequestWrapper(HttpServletRequest request) {
        super(request);
        this.request = request;
    }
    @Override
    public String getParameter(String name) {
        // 根据请求方式不同,去处理:
        // 获得请求方式:
        String method = request.getMethod();
        if("get".equalsIgnoreCase(method)){
            String value = null;
            try {
                value = new String(request.getParameter(name).getBytes("ISO-8859-1"),"UTF-8");
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
            return value;
        }else if("post".equalsIgnoreCase(method)){
            try {
                request.setCharacterEncoding("UTF-8");
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
        }
        return super.getParameter(name);
    }
}

public class EncodingFilter implements Filter{

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) request;
        MyHttpServletRequestWrapper myReq = new MyHttpServletRequestWrapper(req);
        chain.doFilter(myReq, response);
    }

    @Override
    public void destroy() {
        
    }

}