为什么不显示 cookie 值

Question

我们得到了将字母转换为 phone 数字的练习。我有两个 servlet，一个从表单读取输入并将信息存储在会话和 cookie 中（按照我们教授的指示），另一个 servlet 的工作是输出存储在会话对象和 cookie 中的值。问题是每次我输入的东西都不会立即显示出来。

示例：

输入：0922-ABCDEFG |输出：-2223334
输入 2：0912-ABCDEFG |输出：0922-2223334
输入 3：-ABCDEFG |输出：0912-2223334
输入 4：0917-ABCDEFG |输出：- 2223334

这是两个 servlet 的代码：

package com.telco.process;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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;

/**
 * Servlet implementation class ConvertServlet
 */
@WebServlet("/Convert")
public class ConvertServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private String num;
    private String telco;
    private HttpSession session;
    private Cookie cTelco;
    private RequestDispatcher rd;

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
    {
        String convertedNum = "";
        session = request.getSession();
        num = request.getParameter("number");
        telco = request.getParameter("telco");
        rd = request.getRequestDispatcher("Display");

        if (num != null || num != "")
        {
            for (byte i = 0; i < num.length(); i++)
            {
                switch(num.charAt(i))
                {
                    case 'A':
                    case 'B':
                    case 'C': convertedNum += "2"; break;
                    case 'D': 
                    case 'E':
                    case 'F': convertedNum += "3"; break;
                    case 'G':
                    case 'H': 
                    case 'I': convertedNum += "4"; break;
                    case 'J':
                    case 'K':
                    case 'L': convertedNum += "5"; break;
                    case 'M':
                    case 'N':
                    case 'O': convertedNum += "6"; break;
                    case 'P':
                    case 'Q':
                    case 'R':
                    case 'S': convertedNum += "7"; break;
                    case 'T':
                    case 'U':
                    case 'V': convertedNum += "8"; break;
                    case 'W':
                    case 'X':
                    case 'Y':
                    case 'Z': convertedNum += "9"; break;
                }
            }

            session.setAttribute("number", convertedNum);
            cTelco = new Cookie("telco", telco);
            response.addCookie(cTelco);
        }
        rd.forward(request, response);
    }

}

小服务程序 2：

package com.telco.process;

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

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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;

@WebServlet("/Display")
public class DisplayNumber extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        PrintWriter pw = response.getWriter();
        Cookie ck[] = request.getCookies();
        pw.println("The converted number is " + ck[1].getValue() + "-" + request.getSession(false).getAttribute("number")); 
    }
}

Answer 1

您应该从浏览器端进行调查：查看发送的 HTTP headers。

此外 Cookie ck[] = request.getCookies() 是一个数组，但您只显示第二个元素 ck[1]

为什么不显示 cookie 值

Why doesn't the cookie value get displayed

java

cookies

servlets

web-applications