在程式裡怎麼儲存使用者的資料？ 資料存在客戶端：cookie 可以用購物車的功能類比。 cookie是客戶端技術，程式把每個使用者的資料以cookie的形式寫給使用者各自的瀏覽器。當使用者再去訪問伺服器中的web資源時，就會帶著各自的資料去。這樣web資源處理的就是使用者各自的資料了。
下面寫一個簡單的例子，使用cookie顯示上一次的訪問時間：
// 顯示上一次的訪問時間
private void showLastAccessTime(HttpServletRequest request, HttpServletResponse response) throws IOException {
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
out.print("您上次訪問的時間是：");
//獲得使用者的時間cookie
Cookie[] cookies = request.getCookies();
for (int i = 0; cookies != null && i < cookies.length; i++) {
if(cookies[i].getName().equals("lastAccessTime")){
long cookieValue = Long.parseLong(cookies[i].getValue());
SimpleDateFormat format = new SimpleDateFormat("hh:mm:ss");
Date date = new Date(cookieValue);
out.print(format.format(date));
}
}
//給使用者返回最新的訪問時間
Cookie cookie = new Cookie("lastAccessTime",System.currentTimeMillis()+"");
cookie.setMaxAge(1*30*24*3600);
cookie.setPath("/cookies");
response.addCookie(cookie);
}
複製程式碼Cookie細節：
- Cookie是map
- web站點可以傳送多個cookie，瀏覽器可儲存多個cookie
- 瀏覽器一般可存放300個cookie，每個站點最多存放20個。每個cookie的大小限制為4kb。
- 如果建立一個cookie傳送給瀏覽器，預設情況是一個會話級別的cookie，使用者退出瀏覽器後即被刪除。若希望將瀏覽器儲存到硬碟上，需要設定maxAge，並給出一個以秒為單位的時間。設為0，則是刪除該cookie。
- 注意，刪除cookie時path必須一致，否則不會刪除。
刪除cookie：
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
Cookie cookie = new Cookie("lastAccessTime",System.currentTimeMillis()+"");
cookie.setMaxAge(0);
cookie.setPath("/cookies");
response.addCookie(cookie);
response.sendRedirect("/cookies");
}
複製程式碼下面是一個使用cookie完成購物車的例項：
首頁
/**
* Created by yun on 2017/5/6.
* 代表購物車網站首頁
*/
public class CookieDemo1 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
//輸出網站所有商品
out.write("本網站有如下商品：<br/>");
Map<String, Book> map = DB.getAll();
for (Map.Entry<String, Book> entry : map.entrySet()) {
Book book = entry.getValue();
out.print("<a href='/CookieDemo2?id=" + book.getId() + "' target='_blank'>" + book.getName() + "</a><br/>");
}
//顯示使用者曾經看到過的商品
out.write("<br/>"+"您曾經看過如下商品有如下商品：<br/>");
Cookie[] cookies = request.getCookies();
for (int i = 0; cookies != null && i < cookies.length; i++) {
if(cookies[i].getName().equals("bookHistory")){
String[] ids = cookies[i].getValue().split("a"); //轉義，是為了防止，和正規表示式中的定義衝突
for(String id:ids){
Book book = (Book) DB.getAll().get(id);
out.print(book.getName()+"</br>");
}
}
}
}
}
class DB {
private static LinkedHashMap<String,Book> map = new LinkedHashMap(); //連結串列map，方便按序列輸出
static {
map.put("1", new Book("1", "heinika的程式設計之路", "陳利津", "一場有趣的旅程！"));
map.put("2", new Book("2", "javaweb開發", "張孝祥", "好書"));
map.put("3", new Book("3", "全棧工程師之路", "Terry", "全棧！！全棧！！"));
map.put("4", new Book("4", "shell大全", "陳利津", "一場有趣的旅程！"));
map.put("5", new Book("5", "heinika的成神之路", "陳利津", "一場有趣的旅程！"));
}
public static Map<String,Book> getAll() {
return map;
}
}
class Book {
private String id;
private String name;
private String author;
private String description;
public Book() {
}
public Book(String id, String name, String author, String description) {
this.id = id;
this.name = name;
this.author = author;
this.description = description;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
}
複製程式碼詳情頁
/**
* Created by yun on 2017/5/6.
* 物品詳情頁
*/
public class CookieDemo2 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
//根據使用者帶貨來的id，顯示商品的詳細資訊
String id = request.getParameter("id");
Map<String, Book> map = DB.getAll();
Book book = map.get(id);
PrintWriter out = response.getWriter();
out.print(book.getId() + "<br/>");
out.print(book.getName() + "<br/>");
out.print(book.getAuthor() + "<br/>");
out.print(book.getDescription() + "<br/>");
//構建cookie，寫回給瀏覽器
String cookieValue = buildCookie(id, request);
Cookie cookie = new Cookie("bookHistory", cookieValue);
cookie.setMaxAge(1 * 30 * 24 * 3600);
cookie.setPath("/");
response.addCookie(cookie);
out.print("<a href='/CookieDemo1'>返回首頁</a>");
}
private String buildCookie(String id, HttpServletRequest request) {
//bookHistory=null 1 1
//bookHistory=2,1,5 1 1,2,5
//bookhistory=2,5,4 1 1,2,5
//bookHistory=2,5 1 1,2,5
Cookie[] cookies = request.getCookies();
String bookHistory = null;
for (int i = 0; cookies != null && i < cookies.length; i++) {
if (cookies[i].getName().equals("bookHistory")) {
bookHistory = cookies[i].getValue();
}
}
if (bookHistory == null) {
return id;
}
String[] ids = bookHistory.split("a");
LinkedList<String> idList = new LinkedList(Arrays.asList(ids)); //為增刪改查提高效能
if (idList.contains(id)) {
idList.remove(id);
} else {
if (idList.size() == 3) {
idList.removeLast();
}
}
idList.addFirst(id);
StringBuffer sb = new StringBuffer();
for (String bid : idList) {
sb.append(bid + "a");
}
return sb.deleteCharAt(sb.length() - 1).toString();
}
}
複製程式碼