cookie实现浏览记录部分逻辑代码的问题？

Question

工具类模拟数据库中的书籍信息：

public class BookDB {
    private static Map<String, Book> books = new HashMap<String, Book>();
    
    static {
        books.put("1", new Book("1","Java","99.9","javaer","no.1 language"));
        books.put("2", new Book("2","C++","9.9","c++er","no.2 language"));
        books.put("3", new Book("3","PHP","0.9","phper","useless"));
        books.put("4", new Book("4","JavaScript","19.9","JSer","666"));
        books.put("5", new Book("5","swift","9.9","appler","iphone"));
    }
    
    public static Map<String, Book> findAllBooks() {
        return books;
    }
    
    public static Book findBookById(String id) {
        return books.get(id);
    }
}

显示所有书籍的servlet:

public class ShowAllBook extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        request.setCharacterEncoding("UTF-8");
        PrintWriter out = response.getWriter();
        
        out.write("<h1>书籍列表</h1>");
        Map<String, Book> books = BookDB.findAllBooks();
        for (Map.Entry<String, Book> book : books.entrySet()) {
            out.write("<a href='"+request.getContextPath()+"/showBookDetail?id="+book.getKey()+"' target='_blank'>"
                        +book.getValue().getName()+"</a><br/>");
        }
        
        out.write("您最近浏览的历史：<br/>");
        Cookie[] cookies = request.getCookies();
        for (int i=0; cookies!=null&&i<cookies.length; i++) {
            if ("historyBookId".equals(cookies[i].getName())) {
                String[] strs = cookies[i].getValue().split("-");
                for (int j=0; j<strs.length; j++) {
                    out.write(BookDB.findBookById(strs[j]).getName() + "<br/>");
                }
            }
        }
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }

}

点击书名跳转到ShowBookDetail的servlet中：

public class ShowBookDetail extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        request.setCharacterEncoding("UTF-8");
        PrintWriter out = response.getWriter();
        
        String id = request.getParameter("id");
        out.println(BookDB.findBookById(id).getName());
        
        String hisId = makeId(id, request);
        Cookie c = new Cookie("historyBookId", hisId);
        c.setPath(request.getContextPath());
        response.addCookie(c);
    }

    private String makeId(String id, HttpServletRequest request) {
        Cookie[] c = request.getCookies();
        if (c == null) {
            return id;
        }
        //返回的id的内容
        String result = "";
        for (int i=0; i<c.length; i++) {
            if ("historyBookId".equals(c[i].getName())) {
                if (c[i].getValue().indexOf(id) == -1) {
                    result = id + "-" + c[i].getValue();
                    break;
                } else if (c[i].getValue().indexOf(id) == 0) {
                    result = c[i].getValue();
                    break;
                } else {
                    result = id;
                    String[] str = c[i].getValue().split("-");
                    for (int j=0; j<str.length; j++) {
                        //遍历cookie(historyBookId)里是否有传入的id
                        if (!id.equals(str[j])) {    
                            result += "-" + str[j];
                        } 
                    }
                    break;
                }
            }
        }
        if (result.length() <= 5) {
            return result;
        } else {
            return result.substring(0, 5);
        }
    }

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

}

在ShowBookDetail代码中，判断之前cookie里的id是否包含了现点击书名传过来的id，里面if判断如果没有，进行的操作。我比较纳闷如果里面已经存在了这个id的话，代码中并没有写该怎么处理，为什么？

Answer 1

Cookie并不提供修改、删除操作。
如果要修改某个Cookie，只需要新建一个同名的Cookie，添加到response中覆盖原来的Cookie。

                    result = id;
                    String[] str = c[i].getValue().split("-");
                    for (int j=0; j<str.length; j++) {
                        //遍历cookie(historyBookId)里是否有传入的id
                        if (!id.equals(str[j])) {    
                            result += "-" + str[j];
                        } 
                    }
                    break;

这段代码已经将新的ID和旧的ID拼接成新的字符串，保存在cookie中。
不知道你问的是不是这个问题。