从JOIN表检索数据到JSP

Question

[我正在学校中开发一个基本的Web应用程序，正在创建一个包含表[学生，雇员，课程和管理的数据库（该表旨在与其他三个表连接）]]]]

当我试图显示一个JOIN表中的寄存器时，我就遇到了问题，我认为我的错误在于如何从JSP的数组列表中检索数据，

DAO方法

public ArrayList<Administration> retreive_course_register(String course_id) {
        Administration register = null;
        Student student = null;
        Course course = null;
        Employee employee = null;

        ArrayList<Administration> register_of_course = new ArrayList<Administration>();
        PreparedStatement statement;
        try {
            statement = connection.prepareStatement("  SELECT s.student_id, s.first_name, s.last_name,s.date_of_birth,s.email,s.password, " + 
                                                    " e.employee_id, e.first_name , e.last_name , e.email, e.hire_date , e.role, e.password, " + 
                                                    " c.course_id, c.course_name, c.class_room , c.start_date," + 
                                                    " a.schedule " + 
                                                    " FROM administration a " + 
                                                    " JOIN students s " + 
                                                    " ON (a.student_id = a.student_id) " + 
                                                    " JOIN employees e" + 
                                                    " ON (a.employee_id = e.employee_id) " + 
                                                    " JOIN courses  c " + 
                                                    " ON (a.course_id = c.course_id) " + 
                                                    " WHERE c.course_id = ? ");
            statement.setString(1, course_id);

            ResultSet result = statement.executeQuery();
            while (result.next()) {
            register = new Administration();
            student = new Student();
            course = new Course();
            employee = new Employee();

            student.setStudentID(result.getString("student_id"));
            student.setFirstName(result.getString("first_name"));
            student.setLastName(result.getString("last_name"));
            student.setDateOfBirth(result.getString("date_of_birth"));
            student.setEmail(result.getString("email"));
            student.setPassword(result.getString("password"));

            course.setCourseID(result.getString("course_id"));
            course.setCourseName(result.getString("course_name"));
            course.setClassRoom(result.getInt("class_room"));
            course.setStartDate(result.getString("start_date"));

            employee.setEmployeeID(result.getString("employee_id"));
            employee.setFirstName(result.getString("first_name"));
            employee.setLastName(result.getString("last_name"));
            employee.setEmail(result.getString("email"));
            employee.setHireDate(result.getString("hire_date"));
            employee.setRole(result.getString("role"));
            employee.setPassword(result.getString("password"));

            register.setStudent(student);
            register.setCourse(course);
            register.setEmployee(employee);
            register.setSchedule(result.getString("schedule"));

            register_of_course.add(register);

            }
        } catch (SQLException e) {
            e.printStackTrace();
        }

        return register_of_course;
    }
Controller

    @WebServlet("/AdministrationController")
    public class AdministrationController extends HttpServlet {

        // Declaring variables
            private static final long serialVersionUID = 1L;
            private static String LIST_OF_REGISTERS = "/Registration.jsp";
            private static String STUDENT_REGISTERS = "/Registers_student.jsp";
            private static String COURSE_REGISTERS = "/Registers_course.jsp";
            private static String EMPLOYEE_REGISTERS = "/Registers_employee.jsp";
            private CourseDAOInterface course_dao; 
            private AdministrationDAOInterface register_dao;// Setting the variable administration DAO to make it a global one
            private String action;  // the string will keep the parameter obtained from the request
                                    // and based on user´s election will call the desired method
        public AdministrationController() throws ServletException, IOException, ClassNotFoundException {
            super();
            register_dao = new AdministrationDAOImplementation();
            course_dao = new CourseDAOImplementation();
        }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            action = request.getParameter("action");
    if (action.equalsIgnoreCase("retreive_course_registers")) { 
                search_course(request,response);
                retreive_course_registered(request,response);
                RequestDispatcher view = request.getRequestDispatcher(COURSE_REGISTERS);
                view.forward(request, response);
            }
    public void retreive_course_registered (HttpServletRequest request, HttpServletResponse response) {
            ArrayList<Administration> registers_course;
            String courseID = request.getParameter("course_id");

            registers_course = register_dao.retreive_course_register(courseID);
            request.setAttribute("Registers_course",registers_course);
        }

public void search_course(HttpServletRequest request, HttpServletResponse response) {
        String courseID = request.getParameter("course_id");//Retrieving the value from the web form 

        request.setAttribute("course", course_dao.readCourse(courseID));//showing the course selected
    }
}
JSP

<form method="post" action="AdministrationController" >
<table>

<tr>
    <td> <h2>Please introduce the course ID:</h2> </td>
    <td><input type="text" name="course_id" value="${course.courseID}" required/></td>
    <td><input  type="submit" value="Submit"></td>
    <td><input  type="hidden" name="action" value="retreive_course_registers"></td>
</tr>

<tr> <td> <b>Course name :</b> <c:out value="${course.courseName}" /> </td> </tr>

<tr> <td> <b>Start Date : </b> <c:out value="${course.startDate}" /> </td> </tr>

<tr> <td> <b>Classroom :  </b> <c:out value="${course.classRoom}" /> </td> </tr>


</table>

<table border=1 style="text-align:center;">
        <thead>
            <tr>
                <th>Student ID</th>
                <th>Student Name</th>
                <th>Schedule</th>
                <th>Teacher Name</th>
                <th>Teacher ID</th>
            </tr>
        </thead>
        <tbody>
            <c:forEach items="${Registers_course}" var="registers_course">
                <tr>
                    <td>${student.studentID}</td>
                    <td>${student.firstName} ${student.lastName}</td>
                    <td>${administration.schedule}</td>
                    <td>${teacher.firstName} ${teacher.firstName}</td>
                    <td>${teacher.employee_ID}</td>

                </tr>
            </c:forEach>
        </tbody>

    </table>
</form>

</body>
</html>
我的输出

[我正在学校中开发一个基本的Web应用程序，正在创建一个包含表[学生，员工，课程和行政管理（此表旨在与其他三个表结合使用）]的数据库，...

Answer 1

用以下内容替换您的查询：