記一次Servlet中getAttribute的錯誤.

package com.ykmimi.order.servlet;

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 com.ykmimi.order.entity.Customers;
import com.ykmimi.order.service.AuthService;

/**
 * Servlet implementation class ShowUserServlet
 */
@WebServlet("/ShowUserServlet")
public class ShowUserServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
     * response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        ///// * 字元編碼設定
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");

        /////* requestURL
        StringBuffer requestURL = request.getRequestURL();
        System.out.println(requestURL);
        String clientIP = request.getRemoteHost();
        System.out.println(clientIP);


        /////* 擷取cookie
        Cookie[] cs = request.getCookies();
        if(cs.length>0){
            for(Cookie c : cs){
                //擷取Cookie的name,key
                String name = c.getName();
                request.setAttribute("name",name);   //在這裡,如果設定(name,name) 則會在下面cid擷取attribute時出現String轉long的異常.是以要明确key值必須是""String類型
                String value = c.getValue();
                request.setAttribute("value",value);
            }
        }


        ///// * 擷取/login傳送過來的long類型值 cid (customer_id)
        long cid = 0;
        cid  = (long)request.getAttribute("cid");
        System.out.println(cid);
//        cid =Long.parseLong(cidStr);
        /////* 擷取使用者id後進行判定,如果不為0的話,将其再進行查詢,傳回使用者的整個執行個體,再次進行傳值
        /////* 并在最終使用者登陸後的顯示界面上顯示使用者資訊及登陸後的服務資訊.
        if (cid > 0) {
            AuthService as = new AuthService();
            /////* 如果這個id比較符合id的規則 即 大于 0, 那麼用它去資料庫檢索這個id的歸屬者的執行個體
            Customers customer = null;
            customer = as.getCustomersInstanceByID(cid);
            request.setAttribute("customerInstance", customer);
            RequestDispatcher rd = request.getRequestDispatcher("/userInfo.jsp");
            rd.forward(request, response);


//            response.sendRedirect("/userInfo.jsp?cid="+cid+"&cname="+customer.getCustomer_name());
        } else if (cid == 0) {
            RequestDispatcher rd = request.getRequestDispatcher("/error.jsp");
            rd.forward(request, response);
        }

    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
     * response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}      

而且在前一個頁面,也就是寫入Cookie的Servlet轉發過來後,cid是在寫如Cookie前的那一個Servlet轉發過來的,而寫Cookie的那個Servlet不用再重複設定setAttribute("cid",cid)

但如果你在中間轉發的那個Servlet又設定"cid"為别的值,那麼最後接受時也會改為别的值.

将程式設計看作是一門藝術，而不單單是個技術。

敲打的英文字元是我的黑白琴鍵，

思維圖紙畫出的是我編寫的五線譜。

當美妙的華章響起，現實通往二進制的大門即将被打開。