【Session】session把id号存在cookie中、session的URL重写把id加载URL上、购物车（关闭浏览器、禁用cookie）

本文链接：https://blog.youkuaiyun.com/wanwan_javaweb/article/details/24781859

本文介绍了Session的基本概念，包括默认存放时间和配置方法，并详细解释了如何通过设置Cookie的有效时间来保持Session，即使在关闭浏览器后也能找回Session。此外，还展示了如何在禁用Cookie的情况下使用URL重写来传递Session ID，最后通过实例演示了如何利用Session实现购物车功能。

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1、session的默认存放时间是30分钟

session的时间可以在web.xml中配置

 <session-config>
  	<session-timeout>60</session-timeout>
  </session-config>

可以采用代码的方式摧毁session

session.invalidate()

2、关闭浏览器仍然可以找到session

session把id号存在cookie中，存储在浏览器的内存中，关闭浏览器，cookie销毁。

我们可以设置cookie的有效时间，这样即使关闭浏览器，用户还可以带着id找到session。

package com.xiaozhi.controller;

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 javax.servlet.http.HttpSession;

public class SessionDemo extends HttpServlet
{
	public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException
	{

		HttpSession session = request.getSession();
		session.setAttribute("name", "洗衣机");
		//获取session的id将其保存在cookie中30分钟
		String id = session.getId();
		Cookie cookie = new Cookie("JSESSIONID", id);
		cookie.setMaxAge(30 * 60);
		cookie.setPath("/HelloJavaWeb");
		response.addCookie(cookie);
	}

	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException
	{
		super.doPost(req, resp);
	}

}

第一次访问会创建两个cookie，session自己创建的cookie放在内存中，程序创建的放在本地硬盘

重启浏览器，浏览器带着cookie来找session，session还是原来的session

3、如果浏览器禁用cookie，那么可以使用URL重写的方式通过URL带着id。

package com.xiaozhi.controller;

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 javax.servlet.http.HttpSession;

public class SessionDemo extends HttpServlet
{
	public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException
	{
		
		HttpSession session = request.getSession();
		session.setAttribute("name", "洗衣机");
		
		String url1=response.encodeURL("/HelloJavaWeb/servlet/BuyServlet");
		String url2=response.encodeURL("/HelloJavaWeb/servlet/PayServlet");
		
		
		response.getWriter().write("<a href="+url1+">buy</a>");
		response.getWriter().write("<a href="+url2+">pay</a>");
	}

	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException
	{
		super.doPost(req, resp);
	}

}

再就是重定向的URL重写是这样子的：

response.encodeRedirectURL(

4、使用session实现购物车功能

ListBookServlet

package com.xiaozhi.controller;


import java.io.IOException;
import java.io.PrintWriter;
import java.io.Serializable;
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;

//首页，列出所有书
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();
		
		//先得到Session才能对URL编码
		request.getSession();
		
		out.print("本站有如下商品<br/>");
		Map <String,Book>map=Db.getAll();
		for(Map.Entry<String, Book> entry:map.entrySet()){
			Book book=entry.getValue();
			
			//URL编码
			String url=response.encodeURL(request.getContextPath()+"/servlet/BuyServlet?id="+book.getId());
			
			String str="<a target=\"_blank\" href='"+url+"'>"+book.getName()+"购买"+"</a><br/>";
			out.print(str);
		}
	}
}
class Db{
	private static Map<String,Book> map=new LinkedHashMap<String,Book>();
	static {
		map.put("1", new Book("1","JavaWeb开发","老k","一本好书"));
		map.put("2", new Book("2","jdbc开发","老张","一本好书"));
		map.put("3", new Book("3","spring开发","老li","一本好书"));
		map.put("4", new Book("4","struts开发","老张","一本好书"));
		map.put("5", new Book("5","android开发","老bi","一本好书"));
	}
	public static Map getAll(){
		return map;
	}
}
class Book implements Serializable{
	private String id;
	private String name;
	private String author;
	private String description;
	
	public Book() {
		super();
    }
	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;
	}	
}

BuyServlet

package com.xiaozhi.controller;

import java.io.IOException;
import java.io.PrintWriter;
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 javax.servlet.http.HttpSession;

public class BuyServlet 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");
		Book book=(Book)Db.getAll().get(id);
		HttpSession session=request.getSession(false);
		
		
		//关闭浏览器仍然能访问到数据
		String cookieId = session.getId();  
        Cookie cookie = new Cookie("JSESSIONID", cookieId);  
        cookie.setMaxAge(30 * 60);  
        cookie.setPath("/HelloJavaWeb");  
        response.addCookie(cookie); 
		        
		        
		//从session中得到用户购买的商品集合
		List <Book> list=(List)session.getAttribute("list");
		if(list==null){
			list=new LinkedList<Book>();
			session.setAttribute("list", list);
		}		
		list.add(book);
		
		String url=response.encodeRedirectURL(request.getContextPath()+"/servlet/ListCartServlet");
		response.sendRedirect(url);		
	}

}

ListCartServlet

package com.xiaozhi.controller;

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

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

public class ListCartServlet extends HttpServlet {
	public void doGet(HttpServletRequest request, HttpServletResponse response)
		throws ServletException, IOException {
		
	response.setContentType("text/html;charset=UTF-8");
	PrintWriter out = response.getWriter();
	
	HttpSession session=request.getSession(false);
	if(session==null){
		out.write("您没有购买任何商品");
		return;
	}
	List<Book> list=(List) session.getAttribute("list");
	out.write("你购买了如下商品"+"<br/>");
	for(Book book:list){
		out.write(book.getName()+"<br/>");
	}			
}

}

关闭浏览器，购物车的东西还在，禁用cookie，也可以实现购物车功能。