大型网站一般都用cookie，因为session的会在客户端生成，是服务器压力增大，下面我来介绍一下，cookie的原理和使用
原理如图
使用方法：如如下代码demo1生成cookie,demo2获得cookie
demo1:
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;
public class CookieDemo1 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
Cookie cookie = new Cookie("lastTime", new Date().toLocaleString());
cookie.setMaxAge(60 * 60);
cookie.setValue(new Date().toLocaleString());
cookie.setPath(request.getContextPath());// 设置的是有效路劲，如果没有设置，那就表示当前路径
System.out.println(request.getContextPath());
response.addCookie(cookie);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
demo2:
package com.itcast.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;
public class CookieDemo2 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
Cookie[] cookie = request.getCookies();
for (int i = 0; cookie != null && i < cookie.length; i++) {
if ("lastTime".equals(cookie[i].getName())) {
response.getWriter().write(cookie[i].getValue());
System.out.println(cookie[i].getValue());
} else if (cookie == null) {
response.getWriter().write("您是首次访问本站");
Cookie[] cookies = request.getCookies();
}
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
cookie普遍应用于购物车，是一个减缓服务器压力的好技术，下面我来用4个类为大家模拟一下买书购物功能：
1.书类javabean
package cn.itcast.cookie.javabean;
public class Book {
private String id;
private String name;
private String author;
private String price;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public Book() {
super();
// TODO Auto-generated constructor stub
}
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 getPrice() {
return price;
}
public void setPrice(String price) {
this.price = price;
}
public Book(String id, String name, String author, String price) {
super();
this.id = id;
this.name = name;
this.author = author;
this.price = price;
}
}
2.书店的模拟类，一般用数据库，但是这里我们模拟一些数据：package cn.itcast.cookie.javabean;
import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.Map;
public class DB {
private static Map<String, Book> books = new LinkedHashMap<String, Book>();
public static Collection<Book> getAll() {
return books.values();
}
static {
books.put("1", new Book("1", "php实战", "老路", "hello"));
books.put("2", new Book("2", "android开发", "老徐", "110"));
books.put("3", new Book("3", "jdbc开发", "老黎", "106"));
books.put("4", new Book("4", "c++算法", "老方", "107"));
}
public static Book Findbook(String bookid) {
return books.get(bookid);
}
}
3.这个类，有两个功能，第一个，显示全部的书，第二个，在你买书后，刷新能显示你曾经浏览过的书
package com.itcast.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Collection;
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 cn.itcast.cookie.javabean.Book;
import cn.itcast.cookie.javabean.DB;
public class ListBookServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();
request.getParameter("id");
// 获得商品
Collection<Book> books = DB.getAll();
// 显示商品
for (Book book : books) {
out.write("<a href='/day07_cookie/servlet/ShowBookInfo?id="
+ book.getId() + "'>" + book.getName() + "</a><br>");
}
String bookHistory = null;
Cookie[] cookies = request.getCookies();
for (int i = 0; cookies != null && i < cookies.length; i++) {
if ("BookHistory".equals(cookies[i].getName())) {
bookHistory = cookies[i].getValue();
break;
}
}
out.write("您浏览过的商品：</br>");
String[] strs = bookHistory.split("\\-");// 将获得的字符串拆分，获取里面的id，用来找到每一本书
for (int j = 0; j < strs.length; j++) {
System.out.println("strs[i]=" + strs[j]);
Book book = DB.Findbook(strs[j]);
out.write(book.getName() + "</br>");
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
4.显示你购买商品的详细信息，并将你所有的购买的商品的id,拼接成一个1-2-3格式的字符串
package com.itcast.servlet;
import java.io.IOException;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;
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 cn.itcast.cookie.javabean.Book;
import cn.itcast.cookie.javabean.DB;
public class ShowBookInfo extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");
String id = request.getParameter("id");
Book book = DB.Findbook(id);
String BookHistory = makeBookHistory(request, book.getId());
response.getWriter().write(
"" + book.getName() + "</br>" + book.getAuthor() + "</br>"
+ book.getPrice() + "</br>");
Cookie cookie = new Cookie("BookHistory", BookHistory);
response.addCookie(cookie);
}
private String makeBookHistory(HttpServletRequest request, String id) {
Cookie[] cookies = request.getCookies();
String BookHistory = null;
for (int i = 0; cookies != null && i < cookies.length; i++) {
if ("BookHistory".equals(cookies[i].getName())) {
BookHistory = cookies[i].getValue();
break;
}
}
if (BookHistory == null) {
return id;
}
String[] strs = BookHistory.split("-");//如果前面获得的id不是null，将返回来的字符串拆分，获得所有的id,存到String[]中
List<String> list = Arrays.asList(strs);
LinkedList<String> ids = new LinkedList<String>();//添加到LinkedList，是为了能按照先后顺序显示
ids.addAll(list);
if (ids.contains(id)) {// 如果有，移除，并加到第一个
ids.remove(id);//
ids.addFirst(id);
}
if (ids.size() == 3) {//最多显示3个浏览过的商品，如果超过，就删除最后一个
ids.remove(ids.size() - 1);
} else {
ids.addFirst(id);
}
StringBuffer sb = new StringBuffer();
for (String str : ids) {//将所有的id，合并成一个1-2-3的字符串，因为一次只能储存一个数据，在cookie中，所以用这个来储存多个id
sb.append(str + "-");
}
sb.deleteCharAt(sb.length() - 1);
return sb.toString();
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}