深入Cookie

Cookie API

javax.servlet.http.Cookie类用于创建一个Cookie，response接口也中定义了一个addCookie方法，它用于在其响应头中增加一个相应的Set-Cookie头字段。同样，request接口中也定义了一个getCookies方法，它用于获取客户端提交的Cookie。Cookie类的方法：

public Cookie(String name,String value)

setValue与getValue方法

setMaxAge与getMaxAge方法

setPath与getPath方法

setDomain与getDomain方法

getName方法

Set-Cookie:username=qiujy;Domain=localhost;path=/

Cookie:username=qiujy;$Path=/jsp_04_servlet

Cookie细节

一个Cookie只能标识一种信息，它至少含有一个标识该信息的名称（NAME）和设置值（VALUE）。

一个WEB站点可以给一个WEB浏览器发送多个Cookie，一个WEB浏览器也可以存储多个WEB站点提供的Cookie。

浏览器一般只允许存放300个Cookie，每个站点最多存放20个Cookie，每个Cookie的大小限制为4KB。

如果创建了一个cookie，并将他发送到浏览器，默认情况下它是一个会话级别的cookie（即存储在浏览器的内存中），用户退出浏览器之后即被删除。若希望浏览器将该cookie存储在磁盘上，则需要使用maxAge，并给出一个以秒为单位的时间。将最大时效设为0则是命令浏览器删除该cookie。

注意，删除cookie时，path必须一致，否则不会删除

Cookie应用

显示用户上次浏览过的商品

package com.hbsi.domain;

public class Book {
private String id;
private String name;
private String author;
private String descript;
public String getId() {
return id;
}
public void setId(String string) {
this.id = string;
}
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 getDescript() {
return descript;
}
public void setDescript(String descript) {
this.descript = descript;
}


}
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package com.hbsi.dao;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

import com.hbsi.domain.Book;
import com.hbsi.util.DBManager;

public class BookDao {
public List<Book> getAll(){
Connection conn=null;
PreparedStatement pt=null;
ResultSet rs =null;

try {
conn=DBManager.getConnection();
String sql="select * from book";
pt=conn.prepareStatement(sql);
rs=pt.executeQuery();
List<Book> list=new ArrayList<Book>();
while(rs.next()){
Book b=new Book();
b.setId(rs.getString("id"));
b.setName(rs.getString("name"));
b.setAuthor(rs.getString("author"));
b.setDescript(rs.getString("descript"));
list.add(b);
}
return list;
} catch (SQLException e) {
throw new RuntimeException(e);
}finally{
DBManager.closeDB(conn, pt, rs);
}
}
public Book getBook(String id){
Connection conn=null;
PreparedStatement pt=null;
ResultSet rs =null;
try {
conn=DBManager.getConnection();
String sql="select * from book where id=?";
pt=conn.prepareStatement(sql);
pt.setString(1, id);

rs=pt.executeQuery();

if(rs.next()){
Book b=new Book();
b.setId(rs.getString("id"));
b.setName(rs.getString("name"));
b.setAuthor(rs.getString("author"));
b.setDescript(rs.getString("descript"));
return b;
}
return null;
} catch (SQLException e) {
throw new RuntimeException(e);
}finally{
DBManager.closeDB(conn, pt, rs);
}
}
public static void main(String [] args){
BookDao db = new BookDao();
Book b = db.getBook("2");
System.out.println(b.getName());
}
}
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package com.hbsi.servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;

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

import com.hbsi.dao.BookDao;
import com.hbsi.domain.Book;

public class CookieDemo1 extends HttpServlet{

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");
PrintWriter out=response.getWriter();
out.print("本网站商品有：<br/>");
BookDao bd=new BookDao();
List<Book> list=bd.getAll();
for(Book book:list){
out.print("<a href='/BookHistory/servlet/CookieDemo2?id="+book.getId()+"'target='_blank'>"+book.getName()+"</a><br/>");
}
out.print("你浏览过的商品：<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(",");
for(String id:ids){
Book book=bd.getBook(id);
out.print(book.getName()+"<br/>");
}
}
}

}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

doGet(request, response);
}

}
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package com.hbsi.servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Iterator;
import java.util.LinkedList;

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

import com.hbsi.dao.BookDao;
import com.hbsi.domain.Book;

public class CookieDemo2 extends HttpServlet{

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");
PrintWriter out=response.getWriter();

String id =request.getParameter("id");
System.out.println(id);
BookDao bd=new BookDao();
Book book=bd.getBook(id);
System.out.println(book);
out.print("书号："+book.getId()+"<br/>");
out.print("书名："+book.getName()+"<br/>");
out.print("作者："+book.getAuthor()+"<br/>");
out.print("描述："+book.getDescript()+"<br/>");

String cookieValue=buildCookValue(id,request);
Cookie cookie =new Cookie("bookhistory",cookieValue);
cookie.setMaxAge(30*24*3600);
cookie.setPath("/BookHistory");
response.addCookie(cookie);
}

private String buildCookValue(String id, HttpServletRequest request) {
String bookhistory=null;
Cookie[] cookies=request.getCookies();
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;
}
LinkedList<String> list=new LinkedList(Arrays.asList(bookhistory.split(",")));
if(list.contains(id)){
list.remove(id);
list.addFirst(id);
}else{
if(list.size()>=3){
list.removeLast();
list.addFirst(id);
}else{
list.addFirst(id);
}
}
StringBuffer sb=new StringBuffer();
for(String bid:list){
sb.append(bid+",");
}
return sb.deleteCharAt(sb.length()-1).toString();
}

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

}