这是我的代码:
<script type="text/javascript">
                                var xmlhttp;
                                $(document).ready(function (){ 
                                    xmlhttp=new XMLHttpRequest();   
                                });
                                function SubmitCommentAJAX(i){alert();
                                    alert(i.parentNode.getElementsByClassName("commentsScroll")[0].innerHTML);
                                    var thecomment=i.parentNode.getElementsByClassName("styled")[0].innerHTML; 
                                    var commentBox=i.parentNode.getElementsByClassName("commentsScroll")[0];
                                    var request="http://localhost:8080/ituned.com/index?Event=Comment&PostTitle=<%=p.getTitle()%>&PostOwner=<%=p.getUsername_of_Owner()%>&comment="+thecomment;
                                    xmlhttp.open("POST",request,true);
                                    xmlhttp.send();
                                    xmlhttp.onreadystatechange=function()
                                     {
                                      if (xmlhttp.readyState==4 && xmlhttp.status==200)
                                        {        
                                          var response=xmlhttp.responseXML.getElementsByTagName("theComment")[0].text;
                                          commentBox.insertBefore(response, commentBox.firstChild);
                                       }
                                     };
                                }
                                </script>
我得到:Cannot call method 'getElementsByTagName' of null for this line:
var response=xmlhttp.responseXML.getElementsByTagName("theComment")[0].text;
servlet 发送了响应,因为在调试器中它说收到了响应,但无论如何这里是 servlet 中的代码:
response.setContentType("text/xml");
        try {
            response.getWriter().println("<theComment>asasasaasa<br></theComment>");
        } catch (IOException e) {
            e.printStackTrace();
        }
浏览器是chrome。谁能告诉我为什么 xmlhttp.responseXML 是空的?