java - getCookies() 获取 cookie 和 session

Question

我有两个 servlet，另一个 servlet 应该从 cookie 和 session 中输出信息(我们教授的说明)。问题是，我尝试使用 getCookies() 从请求对象获取 cookie，但它返回两个对象，第一个对象的名称为“JSESSIONID”及其随附的十六进制代码，第二个对象包含我创建的 cookie。为什么会发生这种情况？ getCookie() 如何单独返回 cookie？

代码如下:

Servlet 1:

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 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");

        Cookie cTelco = new Cookie("telco", telco);
        if (!(num.equals(null)) || !(num.equals("")))
        {
            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);
            response.addCookie(cTelco);
        }
        rd.forward(request, response);
    }

}

Servlet 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();
        System.out.println(ck[0].getValue());
        pw.println("The converted number is " + "-" + request.getSession(false).getAttribute("number"));    
    }
}

Answer 1

JSESSIONID确实是一个cookie，它用于标识 session 。在服务器上创建一个带有 ID 的 session 。服务器将带有 ID 的 cookie (JSESSIONID) 发送到浏览器。然后，浏览器在每次请求时都会将此 JSESSIONID cookie 发送到服务器，服务器使用它来将请求映射到 session 。

编辑:查找 cookie 的一些示例代码:

您应该仅通过名称访问您的 cookie，而不是通过索引。这是一个示例帮助例程，您可以像这样使用它(当然，在实际程序中检查 null):

System.out.println(getCookieByName(request, "telco").getValue());


/**
 * Find a specific HTTP cookie in a request.
 * 
 * @param request
 *            The HTTP request object.
 * @param name
 *            The cookie name to look for.
 * @return The cookie, or <code>null</code> if not found.
 */
protected Cookie getCookieByName(HttpServletRequest request, String name) {
    if (request.getCookies() == null) {
        return null;
    }
    for (int i = 0; i < request.getCookies().length; i++) {
        if (request.getCookies()[i].getName().equals(name)) {
            return request.getCookies()[i];
        }
    }
    return null;
}