对于jsp中的下拉列表，getAttribute()返回null [英] getAttribute() returns null for drop down list in jsp

问题描述

我正在尝试使用getAttribute()将值从数据库传递到下拉菜单.但是，它返回null.

I am trying to pass value from database to drop down menu using getAttribute(). However, it returns null.

这是我的jsp(updateLecturer.jsp)文件:

This is my jsp (updateLecturer.jsp) file:

<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"><%=((LecturerBean)request.getAttribute("LecturerFullname"))%></option>** 
</select>

</label>
</section>

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

这是我的servlet UpdateLecturerServlet.java):

This is my servlet UpdateLecturerServlet.java) :

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

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

                    request.setAttribute("LecturerFullname",lecturerFullname); 

                    RequestDispatcher view = getServletContext().getRequestDispatcher("/updateLecturer.jsp"); 
                    view.forward(request,response);


    }

这是我的UpdateLecturerDAO:

This is my UpdateLecturerDAO :

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

public static LecturerBean selectlecturer(LecturerBean Lbean) {

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



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())
    {
    LecturerBean lecturer = new LecturerBean();
                lecturer.setLecturerFullname(rs.getString("LecturerFullname"));
                lecturer.add(lecturer);
    }


}

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

请帮助:(非常感谢

推荐答案

如果您在请求中设置了这样的属性

If you set some attribute in request like this

request.setAttribute("key",obj);

您可以通过这样的代码片段将其显示在jsp中

You can get it display in jsp by a scriplet like this

<%=request.getAttribute("key")%>

在您的情况下，请检查以下几点

In your case please check the following points

1. 检查以下代码是否为您提供空值.

1. Check whether the following code is giving you a null.

String lecturerFullname = request.getParameter("LecturerFullame"); 如果这为您提供了null，则请检查网址中传递的参数 LecturerFullame .

String lecturerFullname = request.getParameter("LecturerFullame"); If this gives you null then check whether your passing parameter LecturerFullame in url.

在jsp中，请将以下内容强制转换为正确的对象

In the jsp please cast the following to correct object

<option name="lecturerFullname"><%=((String)request.getAttribute("LecturerFullname"))%></option>

让我知道.

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