cookie、session和java过滤器

来源：互联网发布：知乎ALT80 编辑：程序博客网时间：2024/04/30 01:26

基础知识理解：

cookie、session和过滤器通常都是用在web应用中，cookie和session用来保存一定的数据，过滤器Filter则是在浏览器发出请求之后，而后台执行特定的请求之前发生一定的作用。之所以把这三个放一起，是因为有很多时候都会是把他们结合在一起使用，例如有些登陆程序。

cookie是浏览器的机制，session是服务器的机制，但是实际上cookie也是由服务器生成的，之后返回给浏览器的，并不是浏览器本身生成。当浏览器发送某个请求时，如果拥有有效的cookie则会把这个cookie带在一起。

之所有会有cookie的使用，是因为http协议原本是无状态协议，也就是说通过http协议本身，服务器不能判断浏览器是否之前访问过。

Filter和servlet的写法相似，编写相关代码的时候需要实现Filter接口并重写相关的方法，通常更改较多的是doFilter方法。Filter代码写好以后如果需要发生效用，需要像配置servlet一样在web.xml中进行一定的配置。

以下是一个简单的结合cookie、session、Servlet和Filter的登陆示例代码：

定义一个用户实体类，充当数据库数据，这里使用单例模式，保证只存在一个实例对象：

package models;/** * 用户信息实体类 *  * @author tuzongxun123 * */public class UserModel {    private String userName;    private String password;    // 单例模式，保证只有一个用户对象实例    public static UserModel getInstance() {        UserModel user = new UserModel("zhangsan", "123456");        return user;    }    private UserModel(String userName, String pasword) {        this.userName = userName;        this.password = pasword;    }    public String getUserName() {        return userName;    }    public String getPassword() {        return password;    }}

用户登陆输入信息index.jsp界面，在form表单的action中使用jsp的特性获得项目路径：

<%@ page language="java" import="java.util.*" contentType="text/html; charset=utf-8"    pageEncoding="utf-8"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><title>cookieAndFilterTest</title></head><body>     <form action="<%=request.getContextPath() %>/loginServlet" method="post">        userName：<input type="text" name="userName" /></br>        password：<input type="password" name="password" /></br>        <input type="submit" value="login"/>     </form></body></html>

对应的后台servlet：

package servletTest;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.Cookie;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;import models.UserModel;public class LoginServlet extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        this.doPost(req, resp);    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        String userName = req.getParameter("userName");        String password = req.getParameter("password");        // 模拟数据库数据        UserModel user = UserModel.getInstance();        String dbUserName = user.getUserName();        String dbPassword = user.getPassword();        if (dbUserName.equals(userName) && dbPassword.equals(password)) {            // 用户名和密码都匹配，证明登陆成功，设置session和cookie            HttpSession session = req.getSession();            session.setAttribute("userName", userName);            session.setAttribute("password", password);            Cookie cookie = new Cookie("userName", userName);            Cookie cookie2 = new Cookie("password", password);            // 设置cookie的存储时长            cookie.setMaxAge(60);            cookie2.setMaxAge(60);            // 把cookie发送给浏览器            resp.addCookie(cookie);            resp.addCookie(cookie2);            // 转发请求到用户列表            req.getRequestDispatcher("/userList").forward(req, resp);        } else {            // 转发请求到登陆页面            req.getRequestDispatcher("index.jsp").forward(req, resp);        }        ;    }}

上边登陆后跳转的请求：

package servletTest;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import models.UserModel;public class UserListServlet extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        this.doPost(req, resp);    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        UserModel user = UserModel.getInstance();        //在浏览器中打印出用户列表书数据        resp.getWriter().write(                "userName:" + user.getUserName() + "," + "password:"                        + user.getPassword());    }}

项目web.xml配置：

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"    id="WebApp_ID" version="2.5">      <!-- 访问时的项目名称 -->  <display-name>cookieAndFilterTest</display-name>  <!-- servlet配置 -->  <servlet>     <servlet-name>login</servlet-name>     <servlet-class>servletTest.LoginServlet</servlet-class>  </servlet>  <servlet-mapping>     <servlet-name>login</servlet-name>     <url-pattern>/loginServlet</url-pattern>  </servlet-mapping>  <servlet>     <servlet-name>userList</servlet-name>     <servlet-class>servletTest.UserListServlet</servlet-class>  </servlet>  <servlet-mapping>     <servlet-name>userList</servlet-name>     <url-pattern>/userList</url-pattern>  </servlet-mapping>  <!-- 过滤器设置，浏览其发送请求后首先会走这里 -->  <filter>     <filter-name>loginFilter</filter-name>     <filter-class>filterTest.FilterTest</filter-class>  </filter>  <filter-mapping>     <filter-name>loginFilter</filter-name>     <url-pattern>/*</url-pattern>  </filter-mapping>  <!-- 输入项目名访问的默认页面 -->  <welcome-file-list>    <welcome-file>index.jsp</welcome-file>  </welcome-file-list></web-app>

java过滤器代码：

package filterTest;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.http.Cookie;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import models.UserModel;public class FilterTest implements Filter {    @Override    public void destroy() {    }    @Override    public void doFilter(ServletRequest request, ServletResponse response,            FilterChain chain) throws IOException, ServletException {        // 登陆请求、初始请求直接放行        HttpServletRequest req = (HttpServletRequest) request;        HttpServletResponse resp = (HttpServletResponse) response;        String uri = req.getRequestURI();        if ("/cookieAndFilterTest/loginServlet".equals(uri)                || "/cookieAndFilterTest/".equals(uri)) {            // 放行            chain.doFilter(request, response);            return;        }        // 不是登陆请求的话，判断是否有cookie        Cookie[] cookies = req.getCookies();        if (cookies != null && cookies.length > 0) {            String userName = null;            String password = null;            // 判断cookie中的用户名和密码是否和数据库中的一致，如果一致则放行，否则转发请求到登陆页面            for (Cookie cookie : cookies) {                if ("userName".equals(cookie.getName())) {                    userName = cookie.getValue();                }                if ("password".equals(cookie.getName())) {                    password = cookie.getValue();                }            }            UserModel user = UserModel.getInstance();            if (user.getUserName().equals(userName)                    && user.getPassword().equals(password)) {                chain.doFilter(request, response);                return;            } else {                // 重定向到登陆界面                req.getRequestDispatcher("/index.jsp").forward(req, resp);                return;            }        } else {            req.getRequestDispatcher("/index.jsp").forward(req, resp);            return;        }    }    @Override    public void init(FilterConfig arg0) throws ServletException {    }}

1 0