cookie、session和過(guò)濾器通常都是用在web應(yīng)用中，cookie和session用來(lái)保存一定的數(shù)據(jù)，過(guò)濾器Filter則是在瀏覽器發(fā)出請(qǐng)求之后，而后臺(tái)執(zhí)行特定的請(qǐng)求之前發(fā)生一定的作用。之所以把這三個(gè)放一起，是因?yàn)橛泻芏鄷r(shí)候都會(huì)是把他們結(jié)合在一起使用，例如有些登陸程序。
cookie是瀏覽器的機(jī)制，session是服務(wù)器的機(jī)制，但是實(shí)際上cookie也是由服務(wù)器生成的，之后返回給瀏覽器的，并不是瀏覽器本身生成。當(dāng)瀏覽器發(fā)送某個(gè)請(qǐng)求時(shí)，如果擁有有效的cookie則會(huì)把這個(gè)cookie帶在一起。
之所有會(huì)有cookie的使用，是因?yàn)閔ttp協(xié)議原本是無(wú)狀態(tài)協(xié)議，也就是說(shuō)通過(guò)http協(xié)議本身，服務(wù)器不能判斷瀏覽器是否之前訪問(wèn)過(guò)。
Filter和servlet的寫(xiě)法相似，編寫(xiě)相關(guān)代碼的時(shí)候需要實(shí)現(xiàn)Filter接口并重寫(xiě)相關(guān)的方法，通常更改較多的是doFilter方法。Filter代碼寫(xiě)好以后如果需要發(fā)生效用，需要像配置servlet一樣在web.xml中 進(jìn)行一定的配置。
以下是一個(gè)簡(jiǎn)單的結(jié)合cookie、session、Servlet和Filter的登陸示例代碼：
定義一個(gè)用戶(hù)實(shí)體類(lèi)，充當(dāng)數(shù)據(jù)庫(kù)數(shù)據(jù)，這里使用單例模式，保證只存在一個(gè)實(shí)例對(duì)象：
package models; /** * 用戶(hù)信息實(shí)體類(lèi) * * @author tuzongxun123 * */ public class UserModel { private String userName; private String password; // 單例模式，保證只有一個(gè)用戶(hù)對(duì)象實(shí)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; } } 用戶(hù)登陸輸入信息index.jsp界面，在form表單的action中使用jsp的特性獲得項(xiàng)目路徑：
<%@ 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>
對(duì)應(yīng)的后臺(tái)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"); // 模擬數(shù)據(jù)庫(kù)數(shù)據(jù) UserModel user = UserModel.getInstance(); String dbUserName = user.getUserName(); String dbPassword = user.getPassword(); if (dbUserName.equals(userName) && dbPassword.equals(password)) { // 用戶(hù)名和密碼都匹配，證明登陸成功，設(shè)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); // 設(shè)置cookie的存儲(chǔ)時(shí)長(zhǎng) cookie.setMaxAge(60); cookie2.setMaxAge(60); // 把cookie發(fā)送給瀏覽器 resp.addCookie(cookie); resp.addCookie(cookie2); // 轉(zhuǎn)發(fā)請(qǐng)求到用戶(hù)列表 req.getRequestDispatcher("/userList").forward(req, resp); } else { // 轉(zhuǎn)發(fā)請(qǐng)求到登陸頁(yè)面 req.getRequestDispatcher("index.jsp").forward(req, resp); } ; } } 上邊登陸后跳轉(zhuǎn)的請(qǐng)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(); //在瀏覽器中打印出用戶(hù)列表書(shū)數(shù)據(jù) resp.getWriter().write( "userName:" + user.getUserName() + "," + "password:" + user.getPassword()); } } 項(xiàng)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"> <!-- 訪問(wèn)時(shí)的項(xiàng)目名稱(chēng) --> <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> <!-- 過(guò)濾器設(shè)置，瀏覽其發(fā)送請(qǐng)求后首先會(huì)走這里 --> <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> <!-- 輸入項(xiàng)目名訪問(wèn)的默認(rèn)頁(yè)面 --> <welcome-file-list> <welcome-file>index.jsp</welcome-file> </welcome-file-list> </web-app>
java過(guò)濾器代碼：
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 { // 登陸請(qǐng)求、初始請(qǐng)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; } // 不是登陸請(qǐng)求的話(huà)，判斷是否有cookie Cookie[] cookies = req.getCookies(); if (cookies != null && cookies.length > 0) { String userName = null; String password = null; // 判斷cookie中的用戶(hù)名和密碼是否和數(shù)據(jù)庫(kù)中的一致，如果一致則放行，否則轉(zhuǎn)發(fā)請(qǐng)求到登陸頁(yè)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 { // 重定向到登陸界面 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?jī)?nèi)容，希望對(duì)大家學(xué)習(xí)java程序設(shè)計(jì)有所幫助。
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