从servlet显示数据到下拉菜单jsp [英] display data from servlet to drop down menu jsp

问题描述

我试图避免jsp中的java代码用于下拉菜单。我不知道我的代码是否正确（我打赌还有其他错误），但我真正的问题是，我不知道如何让JSP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，然后它会显示选定的讲师信息以更新（好吧，那是另一个故事）。我希望有人能帮帮忙。

这是我的jsp代码：

  < form action =updateLecturerclass =sky-form> 
< header>更新讲师信息< / header> 
< center> 
< fieldset> 
 
< section> 
< label class =select> 
< select name =selectLecturerid =lecturerFullname> 
< option value =0selected disabled> Lecturers Name< / option> 
 **< option name =lecturerFullname>我在这里遇到了问题!!!< / option> ** 
< / select> 
 
< / label> 
< / section> 
 
< / center> 
< footer> 
< center><按钮类型=submitclass =button>更新< /按钮>< / center> 
< / footer> 
< / form> 
  

这是我的servlet（不知道它是否正确）：

  public void doGet（HttpServletRequest请求，HttpServletResponse响应）
 throws ServletException，java.io.IOException {
 
 
试试{
 
 LecturerBean lecturer = new LecturerBean（）; 
 lecturer.setLecturerFullname（request.getParameter（lecturerFullname））; 
 
 response.sendRedirect（updateLecturer.jsp）; 
 
 
 
 $ b catch（Throwable theException）{
 System.out.println（theException）; 
 
 
 $ / code $ / pre 
 
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）{
 
 //准备一些连接对象
 System.out.println（JIJIJI）; 
 Statement stmt = null; 
 
字符串lecturerID = Lbean.getLecturerID（）; 
字符串lecturerFullname = Lbean.getLecturerFullname（）; 
 String lecturerPassword = Lbean.getLecturerPassword（）; 
 
 System.out.println（j444444）; 
 
 
字符串searchQuery =从讲师选择lecturerfullname; 
 
 System.out.println（你的讲师是+ lecturerFullname）; 
 
 System.out.println（Query：+ searchQuery）; 
 
尝试{
 //连接到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）; 
 
 
 //一些异常处理
 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; 
 
 
 $ / code $ / pre 
 
解决方案
传入DAO并从中返回 - 都是一样的。 
此代码也没有任何意义： 
 
 
  while（rs.next（））{
 rs.getString（lecturerFullname）; 
 
  
您需要在<$ c $中创建一个DAO对象的实例c> doGet（）方法，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填充JSP页面中的菜单：
 < select> 
< c：forEach var =lectureritems =$ {lecturerList}> 
< option value =$ {lecturer.id}> $ {lecturer.fullName}< / option> 
< / c：forEach> 
< / select> 
  
 
I am trying to avoid java codes in jsp for drop down menu. i dont know if my codes are correct in the first place (i bet there are other errors) BUT my real problem is, i dont know how to allow drop down menu in JSP to receive data from servlet. Basically I want the user to select any lecturer name from drop down menu, then it will display the chosen lecturer's information to update (well, thats another story). I hope someone can help. Thank you in advance!


this is my jsp code:
<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>
This is my servlet (not sure if its right anyway):
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);
        }
    }
This is my web.xml file :
<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>
This is my 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;

    }

解决方案
What you pass into the DAO and what returns from it - are one and the same.
This code also doesn't make any sense:
while(rs.next()) {
    rs.getString(lecturerFullname);
}
You need to create an instance of the DAO object in the doGet() method, then populate some list and set the query attribute:
req.setAttribute("lecturerList", lecturerList);
RequestDispatcher rd = req.getRequestDispatcher("updateLecturer.jsp");
rd.forward(req, res);
Then populate the menu in the JSP page by using JSTL:
<select>
     <c:forEach var="lecturer" items="${lecturerList}">
          <option value="${lecturer.id}">${lecturer.fullName}</option>
     </c:forEach>
</select> 


                        
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