如何用cookie查看最近看过的书？

import java.io.Serializable;

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public class Book implements Serializable {
private String id;
private String name;
private String price;
private String auth;
private String publish;
private String description;

public Book() {
}

public Book(String id, String name, String price, String auth,
String publish, String description) {
super();
this.id = id;
this.name = name;
this.price = price;
this.auth = auth;
this.publish = publish;
this.description = description;
}

public String getDescription() {
return description;
}

public void setDescription(String description) {
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 getPrice() {
return price;
}
public void setPrice(String price) {
this.price = price;
}
public String getAuth() {
return auth;
}
public void setAuth(String auth) {
this.auth = auth;
}
public String getPublish() {
return publish;
}
public void setPublish(String publish) {
this.publish = publish;
}

}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");
//1.获取要看的书的id,查询数据库找出书,输出书的详细信息
String id = request.getParameter("id");
Book book = BookDao.getBook(id);
if(book==null){
response.getWriter().write("找不到这本书!");
return;
}else{
response.getWriter().write("

书名:"+book.getName()+"

作者:"+book.getAuth()+"

售价:"+book.getPrice()+"

出版社:"+book.getPublish()+"

描述信息:"+book.getDescription()+"

//2.发送cookie保存最后看过的书
// --- 1 --> 1
// 1 --2,1 --> 2,1
// 2,1--3,2,1 --> 3,2,1
// 3,2,1 -- 4,3,2 --> 4,3,2
// 4,3,2 --3,4,2 --> 3,4,2
String ids = "";

Cookie [] cs = request.getCookies();
Cookie findC = null;
if(cs!=null){
for(Cookie c : cs){
if("last".equals(c.getName())){
findC = c;
}
}
}

if(findC == null){
//说明之前没有看过书的记录
ids += book.getId();
}else{
//说明之前有历史看过的书的记录,需要根据历史记录算一个新的记录出来
String [] olds = findC.getValue().split(",");
StringBuffer buffer = new StringBuffer();
buffer.append(book.getId()+",");
for(int i = 0;iString old = olds[i];
if(!old.equals(book.getId())){
buffer.append(old+",");
}
}
ids = buffer.substring(0, buffer.length()-1);
}

Cookie lastC = new Cookie("last",ids);
lastC.setMaxAge(36002430);
lastC.setPath(request.getContextPath());
response.addCookie(lastC);
}