javascript - 通过 ajax 函数调用返回下拉列表

Question

我正在尝试通过 ajax 函数调用返回一个数组列表，并将结果返回到我的 HTML 下拉列表中。
下面是我的 ajax 函数、servlet 代码和 html。
我的下拉列表总是空着。不知道哪里出了问题。

Servlet 代码:

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    Integer p = Integer.parseInt(request.getParameter("studentid"));

    ArrayList<SessionDataBean> result = new ArrayList<>();
    String sessid = null;
    try ( Connection con = JdbcUtil.getConnection()) {
        String sql= "select distinct F.SESSIONID "
                + "from Students F "
                + "where F.studentid = "+p;
        try (Statement st = con.createStatement()) {
            System.out.println(sql);
            ResultSet rs = st.executeQuery(sql);
            while (rs.next()){
                result.add(new SessionDataBean(rs.getString(1)));
            }

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

        }
    catch (Exception e) {
        e.printStackTrace();
    }
    response.setContentType("application/json");
    new Gson().toJson(result, response.getWriter()); 

    }

Ajax函数调用代码:

function listSession(){
  var name = document.getElementById("studentid").value;      
  $.ajax({
        url : "<%=context%>/ListSessionsServlet?studentid=" + name,
        type : "POST",
        async : false,
        dataType: "json",
          success : function(data) {
              var toAppend = '';
              $.each(data,function(i,o){
                  toAppend += '<option>'+o.id+'</option>';  <---issue might be here?
                 });

                $('#sessid').append(toAppend);
          }  
    });
 }

HTML代码:

    <div class="cell">
        Select Session for Student
        <div class="input-control select mutiple full-size">
            <select id="sessid" name="sessid">
            </select>

        </div>
    </div>

Answer 1

服务器期待一个POST参数"studentid"在

Integer p = Integer.parseInt(request.getParameter("studentid"));

虽然"name"通过了。替代

url : "<%=context%>/ListSessionsServlet?studentid=" + name

对于

url : "<%=context%>/ListSessionsServlet?name=" + name