记一次Servlet中getAttribute的错误.

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 {

        ///// * 字符编码设置
        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);

        /////* 获取cookie
        Cookie[] cs = request.getCookies();
        if(cs.length>0){
            for(Cookie c : cs){
                //获取Cookie的name,key
                String name = c.getName();
                request.setAttribute("name",name);   //在这里,如果设置(name,name) 则会在下面cid获取attribute时出现String转long的异常.所以要明确key值必须是""String类型
                String value = c.getValue();
                request.setAttribute("value",value);
            }
        }

        ///// * 获取/login传送过来的long类型值 cid (customer_id)
        long cid = 0;
        cid  = (long)request.getAttribute("cid");
        System.out.println(cid);
//        cid =Long.parseLong(cidStr);
        /////* 获取用户id后进行判定,如果不为0的话,将其再进行查询,返回用户的整个实例,再次进行传值
        /////* 并在最终用户登陆后的显示界面上显示用户信息及登陆后的服务信息.
        if (cid > 0) {
            AuthService as = new AuthService();
            /////* 如果这个id比较符合id的规则 即 大于 0, 那么用它去数据库检索这个id的归属者的实例
            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);
    }

}

而且在前一个页面,也就是写入Cookie的Servlet转发过来后,cid是在写如Cookie前的那一个Servlet转发过来的,而写Cookie的那个Servlet不用再重复设置setAttribute("cid",cid)

但如果你在中间转发的那个Servlet又设置"cid"为别的值,那么最后接受时也会改为别的值.