Java——Web開發之Cookie的使用
阿新 • • 發佈：2018-11-27
Cookie：是伺服器給客戶端，並且儲存在客戶端上的一份小資料。
- 應用場景：自動登陸，瀏覽記錄，購物車
- http請求是無狀態的。客戶端與伺服器在通訊的時候，是無狀態的，其實就是在客戶端在第二次來訪的時候，伺服器根本就不知道客戶端以前有沒有來訪問過。為了更好的使用者體驗，更好的互動，其實從公司層面講，就是為了更好的收集使用者習慣。
- Cookie分類：
- 會話Cookie：預設情況下，關閉了瀏覽器，那麼cookie就會消失
- 持久Cookie：在一定時間內都有效，並且會儲存在客戶端上
- cookie.setMaxAge(0); //設定將cookie立即刪除
- Cookie的安全問題：由於Cookie會儲存在客戶端上，所以有安全隱患；Cookie的大小與個數有限制
- 簡單使用過程：
- 傳送cookie給客戶端
- 給響應新增一個cookie
- 獲取Cookie，獲取客戶端帶過來的cookie
示範程式碼給出~
Cookie_1.java
package c.Cookie; 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; /** * Servlet implementation class Cookie_1 */ public class Cookie_1 extends HttpServlet { /** * */ private static final long serialVersionUID = 1L; protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //1.Cookie的簡單使用，傳送cookie給客戶端 //是伺服器傳送給客戶端並且儲存在客戶端上的一份小資料 response.setContentType("text/html;charset=utf-8"); /* 方法引數要物件時就給物件 建立物件的幾種方法： 1.直接new 2.單例模式或者提供靜態方法 3.工廠模式構建 stu StuFactory StuBuilder */ Cookie c=new Cookie("aa", "bb"); //給響應新增一個cookie response.addCookie(c); response.getWriter().write("請求成功！"); //在客戶端收到的資訊裡面，響應頭中多了一個欄位Set-Cookie：aa=bb //2.獲取Cookie，獲取客戶端帶過來的cookie Cookie[] cookies=request.getCookies(); if(cookies!=null){ for (Cookie cookie : cookies) { String cookieName=cookie.getName(); String cookieValue=cookie.getValue(); System.out.println(cookieName+"="+cookieValue); } } } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub } }
實現給客戶端多個cookie，設定cookie的有效期的程式碼~
Cookie_2.java
package c.Cookie; 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; public class Cookie_2 extends HttpServlet { private static final long serialVersionUID = 1L; protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //1.先寫cookie,可以給客戶端多個cookie Cookie cookie=new Cookie("qq", "22"); response.addCookie(cookie); Cookie cookie4=new Cookie("age", "12"); response.addCookie(cookie4); //去客戶端傳送過來的cookie Cookie[] cookies=request.getCookies(); if(cookies!=null){ for (Cookie cookie2 : cookies) { System.out.println(cookie2.getName()+"="+cookie2.getValue()); } } //2.cookie的有效期。預設情況下，關閉瀏覽器，cookie就沒有了(針對沒有設定cookie的有效期) //expiry——設定以秒為單位的有效期，正值表示在這個數字過後cookie會失效，負值表示關閉瀏覽器就會失效，預設是-1 int expiry=60*60*24*7; cookie.setMaxAge(expiry); //用於指定只有請求了指定的域名，才會帶上該cookie cookie.setDomain(".bcd.com"); //只有訪問該域名下的JavaWeb_2的這個路徑才會帶cookie cookie.setPath("/JavaWeb_2"); //賦一個新的值 cookie.setValue("rr"); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub } }
小案例：獲取最近訪問時間~
login.html
<!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>Insert title here</title>
</head>
<body>
獲取最近訪問時間<br>
<form action="Cookie_3">
賬號：<input type="text" name="username" /><br>
密碼：<input type="text" name="password" /><br>
<input type="submit" value="登陸" /><br>
</form>
</body>
</html>CookieUtil.java
package cookie.util;
import javax.servlet.http.Cookie;
public class CookieUtil {
public static Cookie findCookie(Cookie[] cookies,String name){
if(cookies!=null){
for (Cookie cookie : cookies) {
if(name.equals(cookie.getName())){
return cookie;
}
}
}
return null;
}
}Cookie_3.java
package c.Cookie;
import java.io.IOException;
import java.util.Date;
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 cookie.util.CookieUtil;
/*
獲取最近訪問時間
*/
public class Cookie_3 extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");
String username=request.getParameter("username");
String password=request.getParameter("password");
if("admin".equals(username)&&"123".equals(password)){
//獲取cookie
Cookie[] cookies=request.getCookies();
//從數組裡找出想要的cookie
Cookie cookie= CookieUtil.findCookie(cookies, "last");
if(cookie==null){
//第一次登陸無cookie
Cookie cookie2=new Cookie("last",System.currentTimeMillis()+"");
cookie2.setMaxAge(60*60);
response.addCookie(cookie2);
response.getWriter().write("歡迎登陸！");
}else{
//第二次登陸，有cookie
//1.獲取以前的cookie
long lastVisitTime=Long.parseLong(cookie.getValue());
//2.輸出到介面
//歡迎登陸！上次來訪時間為：Wed Nov 14 20:16:02 CST 2018
response.getWriter().write("歡迎登陸！"+"上次來訪時間為："+new Date(lastVisitTime));
//3.重置登陸時間
cookie.setValue(System.currentTimeMillis()+"");
response.addCookie(cookie);
}
}else{
response.getWriter().write("登陸失敗！");
}
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
}
}