cookie记录浏览记录
HashMap也是我们使用非常多的Collection，它是基于哈希表的 Map 接口的实现，以key-value的形式存在。在HashMap中，key-value总是会当做一个整体来处理，系统会根据hash算法来来计算key-value的存储位置，我们总是可以通过key快速地存、取value。下面就来分析HashMap的存取。
javabean.java
定义Book类的五个属性
package Book.bean;
public class Book {
private String id;
private String bookName;
private String author;
private float price;
private String description;
//带参数的构造函数
public Book(String id, String bookName, String author, float price,
String description) {
this.id = id;
this.bookName = bookName;
this.author = author;
this.price = price;
this.description = description;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getBookName() {
return bookName;
}
public void setBookName(String bookName) {
this.bookName = bookName;
}
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
public float getPrice() {
return price;
}
public void setPrice(float price) {
this.price = price;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
@Override
public String toString() {
return "Book [id=" + id + ", bookName=" + bookName + ", author="
+ author + ", price=" + price + ", description=" + description
+ "]";
}
}
BookUtils.java
存取书的内容，利用hashMap来存取数据
package Book.utils; import java.util.HashMap;
import java.util.Map; import Book.bean.Book; //书放到数据库中的实现类
public class BookUtils { //为了方便，创建一个静态的Map
private static Map<String,Book> map = new HashMap<String,Book>();
//静态块
static{
map.put("", new Book("","降龙十1掌","金庸1",,"武功绝学降龙十1掌"));
map.put("", new Book("","降龙十2掌","金庸2",,"武功绝学降龙十2掌"));
map.put("", new Book("","降龙十3掌","金庸3",,"武功绝学降龙十3掌"));
map.put("", new Book("","降龙十4掌","金庸4",,"武功绝学降龙十4掌"));
map.put("", new Book("","降龙十5掌","金庸5",,"武功绝学降龙十5掌"));
map.put("", new Book("","降龙十6掌","金庸6",,"武功绝学降龙十6掌"));
map.put("", new Book("","降龙十7掌","金庸7",,"武功绝学降龙十7掌"));
map.put("", new Book("","降龙十8掌","金庸8",,"武功绝学降龙十8掌"));
map.put("", new Book("","降龙十9掌","金庸9",,"武功绝学降龙十9掌"));
map.put("", new Book("","降龙十掌","金庸10",,"武功绝学降龙十掌"));
map.put("", new Book("","降龙十1掌","金庸11",,"武功绝学降龙十1掌"));
}
//拿取书
public static Map<String,Book> getAllBook(){
return map;
}
//获取一本书
public static Book getBookById(String id){
return map.get(id);
}
}
showAllBook.java
读取并显示书籍信息
package Book.servlet; import java.io.IOException;
import java.io.PrintWriter;
import java.util.Map; 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 Book.bean.Book;
import Book.utils.BookUtils; public class showAllBook extends HttpServlet { /**
* 1.显示所有的书
* 2.显示浏览的历史记录
* The doGet method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { request.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter(); out.write("书架：<br>");
//1.显示所有的书
Map<String,Book> map = BookUtils.getAllBook();
//遍历集合 foreach
for (Map.Entry<String, Book> entry : map.entrySet()) {
//拿到每一本书的id
String id = entry.getKey();
//拿到每一本书
Book book = entry.getValue();
//output book name
//客户端跳转
out.write(book.getBookName() + " <a href='" + request.getContextPath() + "/servlet/ShowDetail?id=" + id + " '>显示详细信息</a><br>"); } out.write("<br><br><br>");
//显示浏览的历史记录:cookie的名字定义为history : 值的形式：1-2-3
//拿到cookie，
Cookie[] cs = request.getCookies();
//for
for (int i = ; cs != null && i < cs.length; i++) {
Cookie c = cs[i];
if("history".equals(c.getName())){
//show
out.write("你的浏览记录：<br>");
//got cookie
String value = c.getValue();
//根据形式来拆分成数组
String [] ids = value.split("-");
//show the book
for (int j = ; j < ids.length; j++) {
Book b = BookUtils.getBookById(ids[j]);
out.write(b.getBookName() + "<br>");
}
}
} } /**
* The doPost method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { doGet(request, response);
} }
ShowDetail.java
1.显示书的详细信息： 获取传递过来的 id ，通过BookUtils来获取书的全部信息
2.显示浏览记录 ： 获取传递过来的cookie，分析处理cookie
package Book.servlet; import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.LinkedList; 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 Book.bean.Book;
import Book.utils.BookUtils; /**
* 1.显示书的详细信息
* 2.发送历史浏览记录
* @author kj
*
*/
public class ShowDetail extends HttpServlet { /**
* The doGet method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { request.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
//1.拿到传递的数据
String id = request.getParameter("id");
//根据id查询书
Book book = BookUtils.getBookById(id);
//显示书的信息
out.write(book + " <a href='" + request.getContextPath() + "/servlet/showAllBook'>返回主页继续浏览</a><br>"); //2.发送cookie
//获取历史记录字符串
String history = getHistory(request,id);
//创建cookie
Cookie c = new Cookie("history",history);
c.setMaxAge(Integer.MAX_VALUE);
//设置Cookie存放路径
c.setPath(request.getContextPath());
response.addCookie(c);
} /**
* 获取要发往客户端的历史记录的字符串
* @return
*/
private String getHistory(HttpServletRequest request, String id) {
// 获取字符串的情况
/**
* 历史记录的的cookie被获取 点击的书 结果
* 1. null n n
* 2. 1 1 1
* 3. 1 2 2-1
* 4 1-2 1 1-2
* 5. 1-2 2 2-1
* 6. 1-2 3 3-1-2
* 7. 1-2-3 1 1-2-3
* 8. 1-2-3 2 2-1-3
* 9. 1-2-3 3 3-1-2
* 10 1-2-3 4 4-1-2
*/
//设定一个cookie为空，用来存放获取到的原来的cookie
Cookie history = null;
//拿到所有的cookie
Cookie[] cs = request.getCookies();
//循环判断所有的cookie
for (int i = ; cs!=null && i < cs.length; i++) {
if(cs[i].getName().equals("history")){
history = cs[i];
break;
}
}
//情况1，history为空，没有，就把id添加进去
if(history == null)
return id;
//如果不为空
String value = history.getValue();
System.out.println("----value的长度-----" + value.length()+"***value的值***"+ value);
if(value.length() == ){
//2,3的情况
if(value.equals(id)){
//第一种情况
return id;
}else{
return id + "-" + value;
} }
//剩下的就是大于1的情况了，说明有两个或两个以上的，这就需要拆封成单个字符串了
String[] ids = value.split("-");
////Arrays.asList 返回一个受指定数组支持的固定大小的列表,也可以用for循环
LinkedList<String> list = new LinkedList<String>(Arrays.asList(ids));
//返回此列表中首次出现的指定元素的索引，如果此列表 中不包含该元素，则返回 -1
int index = list.indexOf(id);
//4,5,6的情况 // value的值包括 “a” “-” “b” 所以是3
if(value.length() == ){
System.out.println("######进入 value=3 的情况######");
if(index == -){
//说明没有点击过
list.addFirst(id);
}else{
//说明是点击过的书
list.remove(index);
list.add(id);
}
}
//7,8,9,10的情况，都是三个数
if(value.length() > ){
System.out.println("@@@@@@@进入 value>3 的情况@@@@@@@");
if(index == - ){
list.removeLast();
list.addFirst(id);
}else{
list.remove(index);
list.addFirst(id);
}
} //处理完成后需要将数据输出成字符串的形式
StringBuffer sb = new StringBuffer(list.get());
for (int j = ; j < list.size(); j++) {
sb.append("-" + list.get(j));
} return sb.toString();
} public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { request.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
doGet(request, response);
}
}