为什么我要学java。lang.NullPointerException？

Question

我正在尝试，但我在代码中找不到错误

public static List<Gaming> getGamingByName(String TenSanPham) 
    {
        List<Gaming> gaming = new LinkedList<Gaming>();
        Connection connection = JDBC.JDBCConnection.getJDBCConnection();
        
        String sql ="SELECT * FROM GAMING WHERE TENSANPHAM = ? ";
        
        try {
            PreparedStatement preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, TenSanPham);
            ResultSet rs = preparedStatement.executeQuery();
            
            while (rs.next())
            {
                Gaming gaming1 = new Gaming();
                
                gaming1.setTENSANPHAM(rs.getString("TENSANPHAM"));
                gaming1.setSOLUONG(rs.getString("SOLUONG"));
                gaming1.setGIATIEN(rs.getString("GIATIEN"));
                gaming1.setNGAYSANXUAT(rs.getString("NGAYSANXUAT"));
                gaming1.setXUATXU(rs.getString("XUATXU"));
                gaming1.setABOUT(rs.getString("ABOUT"));
                
                gaming.add(gaming1);
            }
           
        } catch (SQLException e)
        {
            e.printStackTrace();
        }
        return null;

这是编辑的结构 编辑游戏

<%
String TenSanPham = request.getParameter("TenSanPham");

List<Gaming> gamings = new GamingService().getGamingByName(TenSanPham);

for (Gaming gaming : gamings) {
%>
<
<form action="WebJava/EditPost.jsp" method="post">

<p>Ten San Pham: </p>
<input type="text" name="TenSanPham" value="<%=gaming.getTENSANPHAM()%>" readonly="readonly"><br>
<p>So Luong: </p>
<input type="text" name="SoLuong" value="<%=gaming.getSOLUONG()%>"><br>
<p>Gia Tien: </p>
<input type="text" name="GiaTien" value="<%=gaming.getGIATIEN()%>"><br>
<p>Ngay San Xuat: </p>
<input type="text" name="NgaySanXuat" value="<%=gaming.getNGAYSANXUAT()%>"><br>
<p>Xuat Xu: </p>
<input type="text" name="XuatXu" value="<%=gaming.getXUATXU()%>"><br>
<p>About: </p>
<input type="text" name="About" value="<%=gaming.getABOUT()%>"><br>

<input type="submit" value="Edit"><br>
</form>

然后是EditPostName。Jsp

 package QuanLi;
 import java.io.IOException;
 import QuanLi.GameDao;
 import Service.GamingService;
 import jakarta.servlet.RequestDispatcher;
 import jakarta.servlet.ServletException;
 import jakarta.servlet.annotation.WebServlet;
 import jakarta.servlet.http.HttpServlet;
 import jakarta.servlet.http.HttpServletRequest;
 import jakarta.servlet.http.HttpServletResponse;
 @WebServlet(urlPatterns = {"/EditPost123"})
 public class EditPostName extends HttpServlet{
 protected void processRequest(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {
 String TenSanPham = request.getParameter("TenSanPham");
        request.setAttribute("getGamingByName",GameDao.getGamingByName(TenSanPham));

 RequestDispatcher rd = request.getRequestDispatcher("/WebJava/EditGaming.jsp");
        rd.forward(request, response);
        
    }
 @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }
 @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }

} 最后是EditPost。jsp

<%
GamingService gamingService = new GamingService();
Gaming gaming = new Gaming();

gaming.setSOLUONG(request.getParameter("SoLuong"));
gaming.setGIATIEN(request.getParameter("GiaTien"));
gaming.setNGAYSANXUAT(request.getParameter("NgaySanXuat"));
gaming.setXUATXU(request.getParameter("XuatXu"));
gaming.setABOUT(request.getParameter("About"));
gaming.setTENSANPHAM(request.getParameter("TenSanPham"));

/*
String SoLuong = request.getParameter("SoLuong");
String GiaTien = request.getParameter("GiaTien");
String NgaySanXuat = request.getParameter("NgaySanXuat");
String XuatXu = request.getParameter("XuatXu");
String About = request.getParameter("About");
String TenSanPham = request.getParameter("TenSanPham");
*/  
gamingService.updateGaming(gaming);

response.sendRedirect("/ChuyenDeThucTap/WebJava/ListGaming.jsp");

%>

我是一名大三学生，我还有很多缺点，我希望得到大家的帮助。我印象深刻，我知道数组不能遍历一个对象。此外，当从游戏中选择*时，TENSANPHAM=？只会成为一个物体因为TENSANPHAM是关键 enter image description here