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：
<"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"> <> <display-name>cookieAndFilterTest</display-name> <> <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> <> <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> <> <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 { } }
以上就是本文的全部内容，希望对大家学习java程序设计有所帮助。
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