无法访问.jsp文件中导入的.java类中的变量

问题描述 投票:0回答:1

我在将类导入 .jsp 文件时遇到问题。当我尝试导入时,程序继续运行,但无法访问变量。我正在尝试将 GameServlet.java 类导入到 game.jsp 中。

导入如下:

<%@ page import="com.example.TextGame, com.example.GameServlet, java.util.Scanner" %> 

由于某种原因它不起作用

项目结构为:

  • 演示
    • 源代码
      • 主要
        • java
          • com.example
            • GameServlet.java
            • 文字游戏.java
        • 资源
        • 网络应用程序
          • WEB-INF
            • web.xml
          • 游戏.jsp
          • index.jsp
    • 目标
    • pom.xml

我的 .xml 看起来像这样:

xml 文件

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">

    <!-- Servlet Mapping -->
    <servlet>
        <servlet-name>MyServlet</servlet-name>
        <servlet-class>com.example.MyServlet</servlet-class>
    </servlet>
    
    <servlet-mapping>
        <servlet-name>MyServlet</servlet-name>
        <url-pattern>/myservlet</url-pattern>
    </servlet-mapping>

</web-app>

java类:

GameServlet.java

package com.example;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

@WebServlet("/GameServlet")
public class GameServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();
        String playerName = (String) session.getAttribute("playerName");

        session.setAttribute("game", new TextGame());

        response.sendRedirect("game.jsp");
    }
}

TextGame.java

package com.example;

public class TextGame {
    private String currentLocation;

    public TextGame() {
        this.currentLocation = "start";
    }

    public String getCurrentLocation() {
        return currentLocation;
    }

    public void handlePlayerInput(String input) {
        if (input.equalsIgnoreCase("go north")) {
            currentLocation = "north_location";
        } else if (input.equalsIgnoreCase("go south")) {
            currentLocation = "south_location";
        }
    }
}

jsp 文件:

游戏.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%@ page import="com.example.TextGame, com.example.GameServlet, java.util.Scanner" %>
<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Текстова гра - Гравець: ${sessionScope.playerName}</title>
</head>
<body>
    <h1>Вітаємо, ${sessionScope.playerName}!</h1>

    <p>Ви знаходитесь в ${sessionScope.game.currentLocation}.</p>

    <form action="GameServlet" method="post">
        <label for="playerInput">Введіть команду:</label>
        <input type="text" id="playerInput" name="playerInput" required>
        <input type="submit" value="Виконати">
    </form>
</body>
</html>

index.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Текстова гра</title>
</head>
<body>
    <form action="GameServlet" method="post">
        <label for="playerName">Введіть ваше ім'я:</label>
        <input type="text" id="playerName" name="playerName" required>
        <input type="submit" value="Почати гру">
    </form>
</body>
</html>

我尝试导入:

<%@ page import="com.example.TextGame, com.example.GameServlet, java.util.Scanner" %> 

或:

<%@ page import="com.example.TextGame" %>
<%@ page import="com.example.GameServlet" %>
<%@ page import="java.util.Scanner" %>

但是不起作用

java jsp servlets import
1个回答
1
投票

您的 GameServlet 正在从 HttpSession 访问数据,但数据从未存储在那里。

看看用户将如何使用该应用程序。最初他在index.jsp 上,这使得浏览器显示一个表单。用户填写他的用户名,然后在提交时将该用户名发送到下一个网址:GameServlet

GameServlet 现在可以将提交的用户名读取为

request.getParameter("playerName")
并将其存储为
getHttpSession().setAttribute("playerName", request.getParameter("playerName"))

只有在此之后后续页面/servlet 才能够读取会话属性。

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