Question

我试图将字符串从一个servlet传递到另一个servlet，但是我总是在第二个servlet中得到一个空值。我已经将头撞到这个头上了将近2个星期，但无济于事，而且我的想法已经用完了。我已经阅读了此处发布的所有类似问题，但仍然得到一个空值。

这是第一个servlet

@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) 
{
    try 
    {
        HttpSession session = request.getSession();
        String name = (String) session.getAttribute("name");
        int userId = DBConnect.getIdByName(name);
        int lobbyId = DBConnect.insertInLobby(userId);
        request.setAttribute("lobbyId", lobbyId);
        request.getRequestDispatcher("PlatformPairsLobby.jsp").forward(request, response);
    } 
    catch (ServletException | IOException e) 
    {
        logger.error("Error " + e);
    }
}

这是第二个servlet，其名称字符串始终为null。

@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) 
{
    HttpSession session = request.getSession();
    String name = (String) session.getAttribute("name");
    int id = DBConnect.getIdByName(name);
    request.setAttribute("id", id);
    String lobbyId = request.getParameter("lobbyId");
    request.setAttribute("lobbyId", lobbyId);
    response.setContentType("application/x-java-jnlp-file");
    try 
    {
        request.getRequestDispatcher("PairsJnlp.jsp").include(request, response);
    } 
    catch (ServletException | IOException e)
    {
        logger.error("Error " + e);
    }
}

要访问第二个servlet，请在此JSP中使用一个按钮

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@page import="java.awt.List"%>
<%@page import="java.util.*"%>
<%@page import="database.DBConnect"%>
<%@ taglib uri = "http://java.sun.com/jsp/jstl/core" prefix = "c" %>
<html>
<head>
<%  
ArrayList<String> list = (ArrayList<String>) 
request.getAttribute("lobbyList");
Integer lobbyId = (Integer) request.getAttribute("lobbyId");
%>

------------------

window.location.href = 
"http://192.168.100.154:8080/GamePlatformCore/SecondServlet?lobbyId=<%=lobbyId%>";

名称是在其他servlet中设置的。

request.setAttribute("verificare", verificare);
HttpSession session = request.getSession();
session.setAttribute("name", name);

if(request.getServletContext().getAttribute("userMessages")==null)
{
    request.getServletContext().setAttribute("userMessages",new ArrayList<String>());       
}

request.getRequestDispatcher(WELCOME_PAGE).forward(request, response);

Answer 1

您正在使用请求范围属性获取String值，使用以下代码获取Session值：

<% String lobbyId = (String)request.getSession().getAttribute(lobbyId); %>

会话参数为空

1 个答案: