第74節：Java中的Cookie和Session

Servlet · 發表 2019-01-23 23:46:41

摘要：標題圖第74節：第74節：Java中的Cookie和Session ServletContext : 什麼是 ServletContext ,有什麼用哦，怎麼用呢？啟動伺服器後，會給每個應用程式建立一個 ServletCon...

標題圖

第74節：第74節：Java中的Cookie和Session

`ServletContext` :

什麼是 ServletContext ,有什麼用哦，怎麼用呢？

啟動伺服器後，會給每個應用程式建立一個 ServletContext ,並且這個 ServletContext 物件只有一個。可以用於獲取全域性引數，工程下的資源，和存取資料，共享資料。

例子，如何獲取全域性引數，如何獲取工程下的資源，如何進行存取資料，用例子程式碼進行展示。

getServletContext().getInitParams(); 和 getServletConfig().getInitParams();

getServletContext().getRealPath()
getServletContext().getReasourceAsStream()

InputStream is = getClass().getClassLoader().getReasourceAsStream();

相對路徑和絕對路徑

getServletContext().setAttribute()

getServletContext().getAttribute()

獲取登入成功次數

`HttpServletRequest` :

請求物件，用於封裝客戶端提交過來的資料或者資訊。

可以獲取頭資訊，提交過來的資料：

`request.getParameter("name"); // dashucoding url連線拼接

中文亂碼情況

`HttpServletResponse` :

響應物件，伺服器要返回給客戶端的資料

跳轉頁面：

response.setStatus(302);

response.setHeader("Location","success.html");

檔案下載：輸出流和輸入流的對接

下載中文名字的資源：

效果

// index.html
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>

預設servlet去下載<br>
<a href="download/aa.jpg">aa.jpg</a><br>
<a href="download/bb.txt">bb.txt</a><br>
<a href="download/cc.rar">cc.rar</a><br>

<br>手動下載<br>
<a href="Demo01?filename=aa.jpg">aa.jpg</a><br>
<a href="Demo01?filename=bb.txt">bb.txt</a><br>
<a href="Demo01?filename=cc.rar">cc.rar</a><br>
<a href="Demo01?filename=達叔.png">達叔.png</a><br>
</body>
</html>

// Demo01.java
package com.dashucoding.servlet;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class Demo01
 */
public class Demo01 extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
// 獲取要下載的檔名字
String fileName = request.getParameter("filename");
// 獲取這個檔案在tomcat裡面的絕對路徑地址
String path = getServletContext().getRealPath("download/"+fileName);

// 用於使用者下載
response.setHeader("Content-Disposition", "attachment; filename="+fileName);

// 轉化成輸入流
InputStream is = new FileInputStream(path);
OutputStream os = response.getOutputStream();

int len = 0;
byte[] buffer = new byte[1024];
while( (len = is.read(buffer)) != -1) {
os.write(buffer, 0, len);
}

os.close();
is.close();

}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}

}

瀏覽器

// Demo01.java
package com.dashucoding.servlet;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLEncoder;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class Demo01
 */
public class Demo01 extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
// 獲取要下載的檔名字
String fileName = request.getParameter("filename");

// get請求有中文
//byte[] bytes = fileName.getBytes("ISO-8859-1");
//new String(bytes, "UTF-8");
fileName = new String(fileName.getBytes("ISO-8859-1"), "UTF-8");
System.out.println("fileName="+fileName);

// 獲取這個檔案在tomcat裡面的絕對路徑地址
String path = getServletContext().getRealPath("download/"+fileName);

// 對中文的名字進行編碼處理
// 獲取來訪客戶端的型別
String clientType = request.getHeader("User-Agent");

if (clientType.contains("Firefox")) {
fileName = DownLoadUtil.base64EncodeFileName(fileName);
}else {
fileName = URLEncoder.encode(fileName, "UTF-8");
}

// 用於使用者下載
response.setHeader("Content-Disposition", "attachment; filename="+fileName);

// 轉化成輸入流
InputStream is = new FileInputStream(path);
OutputStream os = response.getOutputStream();

int len = 0;
byte[] buffer = new byte[1024];
while( (len = is.read(buffer)) != -1) {
os.write(buffer, 0, len);
}

os.close();
is.close();

}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}

}

// DownLoadUtil
package com.dashucoding.servlet;

import java.io.UnsupportedEncodingException;

import sun.misc.BASE64Encoder;

public class DownLoadUtil {
public static String base64EncodeFileName(String fileName) {
BASE64Encoder base64Encoder = new BASE64Encoder();
try {
return "=?UTF-8?B?"
+ new String(base64Encoder.encode(fileName
.getBytes("UTF-8"))) + "?=";
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
}

效果

登入

效果

// LoginServlet
package com.dashucoding.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class LoginServlet
 */
public class LoginServlet extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
// public void setContextType(String type)
// 設定將傳送到客戶端的響應的內容型別,如果該響應尚未提交,給定內容型別可能包含字元編碼規範,例如
// text/html;charseet=UTF-8,如果在呼叫 getWriter之前呼叫此方法,則只根據給定內容型別設定響應的字元編碼

response.setContentType("text/html;charset=utf-8");

String userName = request.getParameter("username");
String password = request.getParameter("password");

if("admin".equals(userName) && "123".equals(password)) {
response.getWriter().write("登入成功");
}else {
response.getWriter().write("登入失敗");
}

}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}

}

// web
<?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" 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>RequestRedirctionDemo</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.htm</welcome-file>
<welcome-file>default.jsp</welcome-file>
</welcome-file-list>
<servlet>
<description></description>
<display-name>LoginServlet</display-name>
<servlet-name>LoginServlet</servlet-name>
<servlet-class>com.dashucoding.servlet.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LoginServlet</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>
</web-app>

// login
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>

<form action="login">
賬號: <input type="text"name="username"/><br>
密碼: <input type="text"name="password"/><br>
<input type="submit"value="登入"/><br>
</form>
</body>
</html>

效果

// LoginServlet
package com.dashucoding.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class LoginServlet
 */
public class LoginServlet extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
// public void setContextType(String type)
// 設定將傳送到客戶端的響應的內容型別,如果該響應尚未提交,給定內容型別可能包含字元編碼規範,例如
// text/html;charseet=UTF-8,如果在呼叫 getWriter之前呼叫此方法,則只根據給定內容型別設定響應的字元編碼

response.setContentType("text/html;charset=utf-8");

String userName = request.getParameter("username");
String password = request.getParameter("password");

if("admin".equals(userName) && "123".equals(password)) {
// response.getWriter().write("登入成功");
response.setStatus(302);
response.setHeader("Location", "login_success.html");
}else {
response.getWriter().write("登入失敗");
}

}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}

}

效果

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<h1>登入成功!!!</h1>
</body>
</html>

效果

重定向

package com.dashucoding.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class LoginServlet
 */
public class LoginServlet extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
// public void setContextType(String type)
// 設定將傳送到客戶端的響應的內容型別,如果該響應尚未提交,給定內容型別可能包含字元編碼規範,例如
// text/html;charseet=UTF-8,如果在呼叫 getWriter之前呼叫此方法,則只根據給定內容型別設定響應的字元編碼

response.setContentType("text/html;charset=utf-8");

String userName = request.getParameter("username");
String password = request.getParameter("password");

if("admin".equals(userName) && "123".equals(password)) {
// response.getWriter().write("登入成功");
/*response.setStatus(302);
response.setHeader("Location", "login_success.html");*/

// 重定向寫法,重新定位方向
// response.sendRedirect("login_success.html");

// 請求轉發的寫法
request.getRequestDispatcher("login_success.html").forward(request, response);

}else {
response.getWriter().write("登入失敗");
}

}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}

}

`Cookie`

用於自動登入,瀏覽記錄等,是伺服器給客戶端的.

Cookie cookie = new Cookie("a","b");
// 響應
response.addCookie(cookie);

獲取 Cookie

package com.dashucoding.servlet;

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 Demo01
 */
public class Demo01 extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

//Cookie的簡單使用。

//cookie 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");

//傳送cookie給客戶端
Cookie cookie = new Cookie("aa", "bb");
//給響應，新增一個cookie
response.addCookie(cookie);
response.getWriter().write("請求成功了...");



//獲取客戶端帶過來的cookie
Cookie[] cookies = request.getCookies();
if(cookies != null){
for (Cookie c : cookies) {
String cookieName = c.getName();
String cookieValue = c.getValue();
System.out.println(cookieName + " = "+ cookieValue);
}
}

}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}


}

Cookie 是一份小資料,是伺服器給客戶端,儲存在客戶端上的一份小資料.

http 請求是無狀態的.

在響應的時候新增 Cookie

Cookie cookie = new Cookie("name", "value");
// 新增cookie
response.addCookie(cookie);

在客戶端資訊裡,響應頭中多了 Set-Cookie

獲取客戶端帶來的 Cookie

Cookie[] cookies = request.getCookies();
if(cookies != null){
 for(Cookie c : cookies){
String cookieName = c.getName();
String cookieValue = c.getValue();
System.out.println(cookieName + " = " + cookieValue);
 }
}

cookie 過期

public int getMaxAge()
返回以秒為單位指定的 cookie 的最大生存時間.

public void setMaxAge(int expiry)
設定 cookie 的最大生存時間,以秒為單位.

如何顯示上次登入時間

可以進行判斷賬號密碼,如果上次有登入過,那麼顯示上次的登入時間.這裡分兩種情況,獲取帶過來的 cookie 進行判斷,第一種是沒有 cookie 的,第一次登入,輸出登入成功或者失敗,然後給客戶端新增 cookie , new Cookie() ,第二種的登入過的,還是要輸出登入成功或者是失敗,獲取以前的 cookie .時間戳要重置怎麼理解?

package com.dashucoding.servlet;

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 com.dashucoding.util.CookieUtil;

/**
 * Servlet implementation class Demo03
 */
public class Demo03 extends HttpServlet {
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 last-name --- >
Cookie [] cookies = request.getCookies();

//從數組裡面找出我們想要的cookie
Cookie cookie = CookieUtil.findCookie(cookies, "last");

//是第一次登入，沒有cookie
if(cookie == null){

Cookie c = new Cookie("last", System.currentTimeMillis()+"");
c.setMaxAge(60*60); //一個小時
response.addCookie(c);

response.getWriter().write("歡迎您, "+userName);

}else{
//1. 去以前的cookie第二次登入，有cookie
long lastVisitTime = Long.parseLong(cookie.getValue());

//2. 輸出到介面，
response.getWriter().write("歡迎您, "+userName +",上次來訪時間是："+new Date(lastVisitTime));


//3. 重置登入的時間
cookie.setValue(System.currentTimeMillis()+"");
response.addCookie(cookie);
}
}else{
response.getWriter().write("登陸失敗 ");
}

}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}

如何顯示商品瀏覽記錄

獲取提交過來的 id ,把 id 放入到 cookie 裡,跳轉介面.

servlet?id=1;
servlet?id=2;
獲取cookie 1
1#2
setValue("1#2");

jsp

效果

// index.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
 <br>---------1------------<br>
 <%! int a = 123; %>
 <br>---------2------------<br>
 <% int b = 123456; %>
 <br>---------3------------<br>
 <%=a %><br>
 <%=b %>
</body>
</html>

瀏覽記錄

package com.dashucoding.util;

import javax.servlet.http.Cookie;

public class CookieUtil {
/**
* 從一個cookie陣列中找到具體我們想要的cookie物件
* @param cookies
* @param name
* @return
*/
public static Cookie findCookie(Cookie[] cookies , String name){
if(cookies != null){
for (Cookie cookie : cookies) {
if(name.equals(cookie.getName())){
return cookie;
}
}
}
return null;
}
}

<!-- 顯示瀏覽記錄 -->
<%
Cookie[] cookies = request.getCookies();
Cookie cookie = CookieUtil.findCookie(cookies, "history");
// 如果cookie是空,表明沒有瀏覽商品
if(cookie == null){
%>
<h2> 您還沒有瀏覽任何商品! </h2>
<%
}else{
// 不是空,表明有瀏覽記錄
String[] ids = cookie.getValue().split("#");
for(String id : ids){
%>
<li style="width: 150px;height: 216;text-align: center;"><img src="products/1/cs1000<%=id %>.jpg" width="130px" height="130px" /></li>
<%
}
}
%>

package com.dashucoding.servlet;

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 com.dashucoding.util.CookieUtil;

public class ProductInfoServlet extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String id = request.getParameter("id");
Cookie[] cookies = request.getCookies();
Cookie cookie = CookieUtil.findCookie(cookies, "history");
if (cookie==null) {
Cookie cook = new Cookie("history", id);
cook.setMaxAge(60*60*24*7);
response.addCookie(cook);
}else{
String id2 = cookie.getValue();
cookie.setValue(id+"#"+id2);
cookie.setMaxAge(60*60*24*7);
response.addCookie(cookie);
}
response.sendRedirect("product_info.htm");
}


protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}

清除瀏覽記錄

清除 cookie

package com.dashucoding.servlet;

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 ClearHistory
 */
public class ClearHistory extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

// 清除cookie
Cookie c = new Cookie("history", "");
c.setMaxAge(0);
//c.setPath("/demo1");
response.addCookie(c);
response.sendRedirect("product_list.jsp");
}

protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}

}

獲取 cookie ,新增 cookie

request.getCookie();
response.addCookie();

Cookie 分類

cookie.setMaxAge(0); // 刪除
cookie.setMaxAge(100); // 100秒

Cloneable

建立一個 cookie , cookie 是 servlet 傳送到 web 瀏覽器中的少量資訊,這些資訊是由瀏覽器儲存,然後傳送回到伺服器中.

cookie 的值是唯一標識客戶端的,可以用於 cookie 會話管理.一個 cookie 擁有一個名,值,可以有一些可選屬性.但又 cookie 也存在一些問題.瀏覽器支援每個 web 伺服器又20個 cookie ,共有300個 cookie ,每個限制在4KB.

安全隱患,大小與個數限制.

`Session`

會話, Session 是基於 Cookie 的一種會話機制. Cookie 是伺服器返回一部分小資料在客戶端,存放在客戶端上.

Session 是把資料存放在服務端.

interface httpsession

public interface httpSession

常用的方法

package com.dashucoding.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet implementation class Demo01
 */
public class Demo01 extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
HttpSession session = request.getSession();
// 得到會話ID
session.getId();
// 存值
session.setAttribute(name, value);
// 取值
session.getAttribute(name);
// 移植
session.removeAttribute(name);
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}

}

效果

// web.xml
<?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" 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>SessionDemo02</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.htm</welcome-file>
<welcome-file>default.jsp</welcome-file>
</welcome-file-list>
<servlet>
<description></description>
<display-name>LoginServlet</display-name>
<servlet-name>LoginServlet</servlet-name>
<servlet-class>com.dashucoding.servlet.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LoginServlet</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>
</web-app>

// LoginServlet
package com.dashucoding.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class LoginServlet
 */
public class LoginServlet extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
response.setContentType("text/html;charset=utf-8");
response.getWriter().write("收到請求了");
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}

}

// login.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<form action="login">
賬號: <input type="text"name="username"/><br>
密碼: <input type="text"name="password"/><br>
<input type="submit"value="登入"/><br>
</form>
</body>
</html>

session 建立與銷燬

建立 request.getSession();
銷燬 Redis session 存放在伺服器記憶體中的資料
session關閉伺服器銷燬
session會話時間過期

// 可以改的 conf\web.xml 有效期30分鐘
<session-config>
 <session-timeout>30</session-timeout>
</session-config>

package com.dashucoding.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class LoginServlet
 */
public class LoginServlet extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub

response.setContentType("text/html;charset=utf-8");

String sessionid = request.getSession().getId();
System.out.println("sessionid="+sessionid);
// cookid id -> sessionid
response.getWriter().write("收到請求了");
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}

}

session 分析

商品列表新增商品,點選商品新增到購物車,到 servlet .

獲取點選商品標識 id ,儲存到購物車,跳轉介面.

判斷購物車是否有商品,有數量加1,沒有數量等於1.

購物車

效果

package com.dashucoding.servlet;

import java.io.IOException;
import java.util.LinkedHashMap;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class CarServlet
 */
public class CarServlet extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub

response.setContentType("text/html;charset=utf-8");
// 獲取新增到購物車的商品id
int id = Integer.parseInt(request.getParameter("id"));
// cat dog big pig
String [] names = {"cat","dog","big","pig"};
// 取到id對應商品

String name = names[id];

// 獲取購物車存放東西的session
// 把一個map 物件存放到session裡面去,保證只有一次

Map<String, Integer> map = (Map<String, Integer>) request.getSession().getAttribute("cat");

if(map == null) {
// value -> map

map = new LinkedHashMap<String, Integer>();

request.getSession().setAttribute("cat", map);
}

// 判斷購物車裡有沒有該商品
if(map.containsKey(name)) {
// 在原來基礎上 +1
map.put(name, map.get(name)+1);
}else {
map.put(name, 1);
}

response.getWriter().write("<a href='product_list.jsp'><h2>繼續購物</h2></a>");
response.getWriter().write("<a href='cart.jsp'><h2>去購物車結算</h2></a>");
}


protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}

}

<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
 <a href="CarServlet?id=0"><h2>cat</h2></a><br>
 <a href="CarServlet?id=1"><h2>dog</h2></a><br>
 <a href="CarServlet?id=2"><h2>big</h2></a><br>
 <a href="CarServlet?id=3"><h2>pig</h2></a><br>
</body>
</html>

效果

// cart.jsp
<%@page import="java.util.Map"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
 您的購物車商品如下:
 <%
// 獲取到map
Map<String,Integer> map = (Map<String,Integer>)session.getAttribute("cat");
// 遍歷
if(map != null){
for(String key : map.keySet()){
int value = map.get(key);
// key:商品名稱 value:商品名稱
// <h3>名稱： 數量: </h3>
%>
<h3>名稱: <%=key %> 數量: <%=value %></h3><br>
<%
}
}
%>
</body>
</html>

效果

package com.dashucoding.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet implementation class ClearCartServlet
 */
public class ClearCartServlet extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub

HttpSession session = request.getSession();

// cat購物車
session.removeAttribute("cat");
response.sendRedirect("cart.jsp");

}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}

}

<%@page import="java.util.Map"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
 您的購物車商品如下:
 <%
// 獲取到map
Map<String,Integer> map = (Map<String,Integer>)session.getAttribute("cat");
// 遍歷
if(map != null){
for(String key : map.keySet()){
int value = map.get(key);
// key:商品名稱 value:商品名稱
// <h3>名稱： 數量: </h3>
%>
<h3>名稱: <%=key %> 數量: <%=value %></h3><br>
<%
}
}
%>
<a href="ClearCartServlet"><h4>清空購物車</h4></a>
</body>
</html>

效果

public void invalidate()
使用,會話無效,取消對任何繫結到它的物件.
// 強制幹掉會話
// session.invalidate();

小結

cookie和session

Cookie
獲取上一次訪問時間,獲取瀏覽記錄,資料存放在客戶端

Session
會話技術,資料存放在服務端

setAttribute 存放資料
getAttribute 取資料
removeAttribute 移除
getSessionId() 獲取會話id
invalidate() 讓會話失效

response.addCookie(new Cookie())
request.getSession 建立

如果看了覺得不錯

點贊！轉發！

達叔小生：往後餘生，唯獨有你

You and me, we are family !

90後帥氣小夥，良好的開發習慣；獨立思考的能力；主動並且善於溝通

簡書部落格：達叔小生

https://www.jianshu.com/u/c785ece603d1

結語

下面我將繼續對其他知識深入講解，有興趣可以繼續關注
小禮物走一走 or 點贊

第74節：Java中的Cookie和Session

ServletContext :

HttpServletRequest :

HttpServletResponse :

Cookie

Session

小結

結語

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`ServletContext` :

`HttpServletRequest` :

`HttpServletResponse` :

`Cookie`

`Session`