相對於Cookie而言，Session並不經常在伺服器中使用，因為session為每一個瀏覽器使用者建立了一個session，這樣對伺服器的要求無形之中高了很多，而cookie是對每個瀏覽器傳送資料，所以伺服器負擔小，所以大部分瀏覽器還是選擇使用cookie來實現瀏覽記錄的顯示。

當用戶的瀏覽器禁用Cookie的時候，可以使用超連結裡面帶著指定的id去訪問servlet，具體程式碼為response.encodeURL("/");裡面放具體的servlet訪問地址,這樣的話，就能帶著指定的id去訪問從而解決了禁用cookie問題,
如果使用者沒有禁用cookie，則第一次他會將超連結和cookie同時傳送回去，但是，當第二次訪問的時候，伺服器發現他返回了cookie,則就不在重新寫超連結了

本案例是使用session來實現模仿當用戶在首頁點選了商品名字的時候，通過session記錄了各個他點選的商品的名字，然後當選擇結賬的時候，自動將他選擇購買的商品顯示出來，下面上程式碼

第一段程式碼是用來充當首頁的servlet,裡面假設了如果使用者禁用cookie的情況

package com.bird.shopping;

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;
/**
 * @category 模擬網站首頁的servlet用來顯示所有的商品
 * @author Bird
 *
 */
public class ListBookServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setCharacterEncoding("UTF-8");
		response.setContentType("text/html;charset=UTF-8");
		PrintWriter out = response.getWriter();
		
		request.getSession();//注意，一定要得到session，否則無法進行自動的id新增
		
		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();
			String url = response.encodeURL("/Web/servlet/BuyServlet?id="+book.getId()+"");
			out.write(book.getName()+"<a href='"+url+"' target='_blank'>購買</a></br>");
		}
		
	}

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

	}

}

class DB{
	//必須使用連結串列Map進行有序儲存
	private static Map<String,Book> map = new LinkedHashMap<String,Book>();
	static{
		map.put("1", new Book("1","javaweb開發詳解","老張","一本好書!!!"));
		map.put("2", new Book("2","jdbc開發詳解","老張","一本好書!!!"));
		map.put("3", new Book("3","sping開發詳解","老黎","一本好書!!!"));
		map.put("4", new Book("4","struts開發詳解","老宇","一本好書!!!"));
		map.put("5", new Book("5","heibrate開發詳解","老畢","一本好書!!!"));
	}
	
	public static Map<String,Book> getAll(){
		return map;
	}
}

class Book implements Serializable{
	
	private static final long serialVersionUID = 1L;
	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;
	}
	
}	
 

package com.bird.shopping;

import java.io.IOException;
import java.util.ArrayList;
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;

/**
 * @category 購買
 * @author Bird
 *
 */
public class BuyServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		String id = request.getParameter("id");
		Book book = DB.getAll().get(id);
		
		HttpSession session = request.getSession();
		
		//從session獲得使用者儲存的資料（購物車）
		@SuppressWarnings("unchecked")
		List<Book> list = (List<Book>) session.getAttribute("list");
		if(list==null){
			list = new ArrayList<Book>();
			session.setAttribute("list", list);
		}
		
		list.add(book);
		String url = response.encodeRedirectURL(request.getContextPath()+"/servlet/ListCarServlet");
		//request.getRequestDispatcher("/servlet/ListCarServlet").forward(request, response);
		response.sendRedirect(url);
	}

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

	}

}
 

package com.bird.shopping;

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;

/**
 * @category 顯示使用者購買的商品
 * @author Bird
 *
 */
public class ListCarServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setCharacterEncoding("UTF-8");
		response.setContentType("text/html;charset=UTF-8");
		PrintWriter out = response.getWriter();
		
		HttpSession session = request.getSession();
		if(session == null){
			out.write("您沒有購買任何商品");
			return;
		}
		
		out.write("您購買了如下商品:</br>");
		@SuppressWarnings("unchecked")
		List<Book> list = (List<Book>) session.getAttribute("list");
		for(Book book: list){
			out.write(book.getName());
			out.write("</br>");
		}
	}

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

	}

}