cookie、session和過濾器通常都是用在web應用中，cookie和session用來保存一定的數據，過濾器Filter則是在瀏覽器發出請求之后，而后臺執行特定的請求之前發生一定的作用。之所以把這三個放一起，是因為有很多時候都會是把他們結合在一起使用，例如有些登陸程序。
cookie是瀏覽器的機制，session是服務器的機制，但是實際上cookie也是由服務器生成的，之后返回給瀏覽器的，并不是瀏覽器本身生成。當瀏覽器發送某個請求時，如果擁有有效的cookie則會把這個cookie帶在一起。
之所有會有cookie的使用，是因為http協議原本是無狀態協議，也就是說通過http協議本身，服務器不能判斷瀏覽器是否之前訪問過。
Filter和servlet的寫法相似，編寫相關代碼的時候需要實現Filter接口并重寫相關的方法，通常更改較多的是doFilter方法。Filter代碼寫好以后如果需要發生效用，需要像配置servlet一樣在web.xml中 進行一定的配置。
以下是一個簡單的結合cookie、session、Servlet和Filter的登陸示例代碼：
定義一個用戶實體類，充當數據庫數據，這里使用單例模式，保證只存在一個實例對象：
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package models; /** * 用戶信息實體類 * * @author tuzongxun123 * */public class UserModel { private String userName; private String password; // 單例模式，保證只有一個用戶對象實例 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的特性獲得項目路徑：
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<%@ 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> |
對應的后臺servlet：
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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"); // 模擬數據庫數據 UserModel user = UserModel.getInstance(); String dbUserName = user.getUserName(); String dbPassword = user.getPassword(); if (dbUserName.equals(userName) && dbPassword.equals(password)) { // 用戶名和密碼都匹配，證明登陸成功，設置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); // 設置cookie的存儲時長 cookie.setMaxAge(60); cookie2.setMaxAge(60); // 把cookie發送給瀏覽器 resp.addCookie(cookie); resp.addCookie(cookie2); // 轉發請求到用戶列表 req.getRequestDispatcher("/userList").forward(req, resp); } else { // 轉發請求到登陸頁面 req.getRequestDispatcher("index.jsp").forward(req, resp); } ; } } |
上邊登陸后跳轉的請求：
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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列表書數據 resp.getWriter().write( "userName:" + user.getUserName() + "," + "password:" + user.getPassword()); } } |
項目web.xml配置：
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<?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"> <!-- 訪問時的項目名稱 --> <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> <!-- 過濾器設置，瀏覽其發送請求后首先會走這里 --> <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> <!-- 輸入項目名訪問的默認頁面 --> <welcome-file-list> <welcome-file>index.jsp</welcome-file> </welcome-file-list> </web-app> |
java過濾器代碼：
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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 { // 登陸請求、初始請求直接放行 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; } // 不是登陸請求的話，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中的用戶名和密碼是否和數據庫中的一致，如果一致則放行，否則轉發請求到登陸頁面 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內容，希望對大家學習java程序設計有所幫助。
