从 servlet 显示数据到下拉菜单 jsp

Question

我试图避免在 jsp 中为下拉菜单使用 java 代码。我首先不知道我的代码是否正确（我敢打赌还有其他错误）但我真正的问题是，我不知道如何允许 JSP 中的下拉菜单从 servlet 接收数据。基本上我希望用户从下拉菜单中选择任何讲师姓名，然后它将显示所选讲师的信息以进行更新（嗯，那是另一个故事）。我希望有人能帮帮忙。提前谢谢！

这是我的jsp代码：

<form action="updateLecturer" class="sky-form">
<header>Update Lecturer Information</header>
<center>
<fieldset>

<section>
<label class="select">
<select name="selectLecturer" id="lecturerFullname">
<option value="0" selected disabled>Lecturers Name</option>        
**<option name="lecturerFullname">I HAVE PROBLEM IN HERE!!!</option>** 
</select>

</label>
</section>

</center>
<footer>
<center><button type="submit" class="button">Update</button></center>
</footer>
</form>

这是我的 servlet（不确定它是否正确）：

public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, java.io.IOException {


        try {

            LecturerBean lecturer = new LecturerBean();
   lecturer.setLecturerFullname(request.getParameter("lecturerFullname"));

                        response.sendRedirect("updateLecturer.jsp");


        }

        catch (Throwable theException) {
            System.out.println(theException);
        }
    }

这是我的 web.xml 文件：

<servlet>
        <servlet-name>UpdateLecturerServlet</servlet-name>
        <servlet-class>CSP600.UpdateLecturerServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>UpdateLecturerServlet</servlet-name>
        <url-pattern>/updateLecturer</url-pattern>
    </servlet-mapping>

这是我的 DAO：

 static Connection currentCon = null;
    static ResultSet rs = null;

    public static LecturerBean lecturerlogin(LecturerBean Lbean) {

        // preparing some objects for connection
        System.out.println("JIJIJI");
        Statement stmt = null;

        String lecturerID = Lbean.getLecturerID();
        String lecturerFullname = Lbean.getLecturerFullname();
        String lecturerPassword = Lbean.getLecturerPassword();

        System.out.println("j444444");


        String searchQuery = "select lecturerfullname from lecturer";

        System.out.println("Your lecturer is " + lecturerFullname);

        System.out.println("Query: " + searchQuery);

        try {
            // connect to DB
            currentCon = JavaConnectionDB.getConnection();
            stmt = currentCon.createStatement();
            rs = stmt.executeQuery(searchQuery);
           // boolean more = rs.next();

            while(rs.next())
            {
            rs.getString(lecturerFullname);
            }
        }

        catch (Exception ex) {
            System.out.println("Log In failed: An Exception has occurred! " + ex);
        }

        // some exception handling
        finally {
            if (rs != null) {
                try {
                    rs.close();
                } catch (Exception e) {
                }
                rs = null;
            }

            if (stmt != null) {
                try {
                    stmt.close();
                } catch (Exception e) {
                }
                stmt = null;
            }

            if (currentCon != null) {
                try {
                    currentCon.close();
                } catch (Exception e) {
                }

                currentCon = null;
            }
        }

        return Lbean;

    }

Answer 1

您传递到 DAO 的内容和从中返回的内容 - 是一回事。 这段代码也没有任何意义：

while(rs.next()) {
    rs.getString(lecturerFullname);
}

您需要在doGet() 方法中创建DAO 对象的实例，然后填充一些列表并设置查询属性：

req.setAttribute("lecturerList", lecturerList);
RequestDispatcher rd = req.getRequestDispatcher("updateLecturer.jsp");
rd.forward(req, res);

然后使用 JSTL 在 JSP 页面中填充菜单：

<select>
     <c:forEach var="lecturer" items="${lecturerList}">
          <option value="${lecturer.id}">${lecturer.fullName}</option>
     </c:forEach>
</select>