Question

我正在使用eclipse创建一个动态Web项目，遵循MVC设计。我目前正在尝试从我的sql表中获取数据以显示在JSP页面上，但它只是返回为空白。我使用JNDI datasorce连接工作正常。当我将项目部署到服务器时，表头显示正常，但下面没有数据。这是我的代码

JSP代码

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>  
<head>  
<title>View All Students</title>  
</head>  
<body>  

<h1>Students List</h1>  

<table cellpadding="5" border=1>  

<tr valign="bottom">  
<th><%= request.getAttribute("Student_Id") %></th>  
<th>First Name</th>  
<th>Last Name</th>
<th>Week 1</th> 
<th>Week 2</th>
<th>Week 3</th>
<th>Week 4</th>
<th>Week 5</th>
<th>Week 6</th>
<th>Week 7</th>
<th>Week 8</th>
<th>Week 9</th>
<th>Week 10</th>
<th>Week 11</th>
<th>Week 12</th>   
</tr>  
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>  
<c:forEach var="student" items="${viewAllStudents}">  
<tr valign="top">  
<td><p>${student.Student_Id}</td>  
<td><p>${student.firstName}</td>  
<td><p>${student.lastName}</td>
<td><p>${student.Week1}</td>
<td><p>${student.Week2}</td>
<td><p>${student.Week3}</td>
<td><p>${student.Week4}</td>
<td><p>${student.Week5}</td>
<td><p>${student.Week6}</td>
<td><p>${student.Week7}</td>
<td><p>${student.Week8}</td>
<td><p>${student.Week9}</td>
<td><p>${student.Week10}</td>
<td><p>${student.Week11}</td>
<td><p>${student.Week12}</td>
</tr>  
</c:forEach>  

</table>  

</body>  
</html>

Servelt（控制器）代码

    package uk.ac.qub.PTStudentView;

    import java.io.IOException;
    import java.sql.Connection;
    import java.sql.SQLException;
    import java.util.List;

    import javax.naming.Context;
    import javax.naming.InitialContext;
    import javax.naming.NamingException;
    import javax.servlet.ServletConfig;
    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.sql.DataSource;

    import uk.ac.qub.Beans.Student;
    import uk.ac.qub.LoginController.Account;

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

    private DataSource ds;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public PTStudentViewController() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see Servlet#init(ServletConfig)
     */
    public void init(ServletConfig config)  throws ServletException {
        try {
            InitialContext initContext = new InitialContext();

            Context env = (Context) initContext.lookup("java:comp/env");

            ds = (DataSource) env.lookup("jdbc/testdb");

        } catch (NamingException e) {
            throw new ServletException();
        }
    }


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




        try {
            List<Student> viewAllStudents = PTViewStudent.list();
            request.setAttribute("students", viewAllStudents); // Will be available as ${students} in JSP
            request.getRequestDispatcher("ViewAllStudentsPage.jsp").forward(request, response);
        } catch (SQLException e) {
            throw new ServletException("Cannot obtain products from DB", e);
        }
    }

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

    }

Sql statment的类

package uk.ac.qub.PTStudentView;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

import uk.ac.qub.Beans.Student;

public class PTViewStudent {
private static Connection conn;

public PTViewStudent (Connection conn){
    this.conn = conn;
}

public static List<Student> list() throws SQLException{

    String sql = "select * from student where Student_Id = 666";
    PreparedStatement stmt = conn.prepareStatement(sql);

    ResultSet rs = stmt.executeQuery();
    List<Student> viewAllStudents = new ArrayList<>();

    while(rs.next()){
        Student student = new Student();
        student.setId(rs.getInt("Student_Id"));
        student.setFirstName(rs.getString("firstName"));
        student.setLastName(rs.getString("lastName"));
        student.setWeek1(rs.getDouble("Week1"));
        student.setWeek2(rs.getDouble("Week2"));
        student.setWeek3(rs.getDouble("Week3"));
        student.setWeek4(rs.getDouble("Week4"));
        student.setWeek5(rs.getDouble("Week5"));
        student.setWeek6(rs.getDouble("Week6"));
        student.setWeek7(rs.getDouble("Week7"));
        student.setWeek8(rs.getDouble("Week8"));
        student.setWeek9(rs.getDouble("Week9"));
        student.setWeek10(rs.getDouble("Week10"));
        student.setWeek11(rs.getDouble("Week11"));
        student.setWeek12(rs.getDouble("Week12"));
        viewAllStudents.add(student);
    }
    return viewAllStudents;
}

}

谢谢你的帮助

Answer 1

我发现了你的错误！

是的，所以在你的jsp中，你有这行代码
<c:forEach var="student" items="${viewAllStudents}">
这意味着，在请求范围中查找名为viewAllStudents的列表，然后循环遍历所有

但是，在您的实际servlet代码中，这是有效的，你有这个：
List<Student> viewAllStudents = PTViewStudent.list(); request.setAttribute("students", viewAllStudents); // Will be available as ${students} in JSP request.getRequestDispatcher("ViewAllStudentsPage.jsp").forward(request, response);

这也是有效的，但是，您需要将JSTL更改为此 <c:forEach var="student" items="${students}">

无法获取SQL查询结果以显示在JSP Page表中？

1 个答案: