每次按下按钮在客户端聊天的servlets中使用ajax检索消息和值时，都会收到leave page警报？

Question

在我的jsp页面中，我显示了包含文本区域、文本字段和发送按钮的div，只有当我得到sessionId！=“空”。

此外，我有一个确认警报框，用于关闭窗口注销会话。。。

但是，如果我试图检索setsionId、userId等的值，我每次都会收到相同的警报...或者在按start Chat或发送按钮时发送消息以切断...在我的Jsp页面中，

<div id="login">
<form id="indexForm" name="indexForm" action="LoginAction" method="post">
<table>
    <tr>
        <td id="fname" class="fontStyle">First Name :</td>
        <td id="fvalue"><input type="text" id="firstname"
            name="firstname" /></td>
        <td id="lname" class="fontStyle">Last Name :</td>
        <td id="lvalue"><input type="text" id="lastname" name="lastname" /></td>
    </tr>
    <tr>
        <td colspan="4" id="err1" style="color: red">&nbsp;</td>

    </tr>
    <tr>
        <td id="email_id" class="fontStyle">Email Id&nbsp;&nbsp; &nbsp;:</td>
        <td><input type="text" id="email" name="email" /></td>
        <td id="sub" class="fontStyle">Subject
        &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;:</td>
        <td><input type="text" id="subject" name="subject" /></td>
    </tr>

    <tr>
        <td colspan="4">&nbsp;</td>
    </tr>

    <tr>
        <td colspan="4" id="err2" style="color: red">&nbsp;</td>
    </tr>

    <tr>
        <td colspan="4">&nbsp;</td>
    </tr>

    <tr>
        <td></td>
        <td>
        <center><a id="button" href="javascript:getValues();">Start
        chat</a></center>
        </td>
        <td>
        <center><a id="button" href="javascript:logout();">Stop
        chat</a></center>
        </td>
        <td></td>
    </tr>

</table>

</form>
</div>

<div style="display: none;" id="div">
<div><textarea id="textarea" rows="10"></textarea></div>
<div>
<table>
    <tr>
        <td id="msg" class="fontStyle">message :</td>
        <td id="msgvalue"><input size="40" type="text" id="message"
            onkeydown="enterKey()" /></td>
        <td style="width: 5%;"></td>
        <td><!-- <input type="button" value="send" onclick="sendMessage()" /> -->
        <a id="button3" href="javascript:sendMessage();">Send</a></td>
    </tr>
</table>
</div>
</div>

在我的JavaScript中，

window.onbeforeunload = function () {

      return  "Are you Sure want to LOGOUT the session ?";
};

window.onunload = function () {

        if((sessionId != null)&&(sessionId!="null")&& (sessionId != ""))
            logout();
};

function sendMessage(){

    message = document.getElementById("message").value;
    document.getElementById("message").innerText = "";
    try
    {
        xmlhttp.onreadystatechange=function()
        {
            //alert("Status : "+xmlhttp.status+"\nreadyState : "+xmlhttp.readyState);
            if (xmlhttp.readyState==4 && xmlhttp.status==200)
            {


                var checkMsg = decodeURIComponent(xmlhttp.responseText.toString());
                if(checkMsg != "null" && checkMsg != null){
                    //document.getElementById("textarea").innerHTML +=  checkMsg;
                    if(textarea.value == "")
                        textarea.value = checkMsg;
                    else
                        textarea.value += "\n"+ checkMsg  ;
                }
            }
        };
        xmlhttp.open("POST","SendMessageAction?sessionId="+sessionId+"&userId="+userId+"&securekey="+secureKey+"&message="+encodeURIComponent(message)+"&sid"+Math.random(),true);
        xmlhttp.send();
    }
    catch(err)
    {
        alert(err.description);
    }
}

在我的Servlet中，

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

        PrintWriter out = response.getWriter();
        msg = request.getParameter("message");
        //System.out.println("msg -----> : "+msg);
        seckey = request.getParameter("securekey");
        uid = request.getParameter("userId");
        sessionId = request.getParameter("sessionId");
        //counter =Integer.parseInt(request.getParameter("counter"));
        counter = 1;
        protocol = ApplicationInfo.flexProtocol;

        message = new SendMessage();
        message.send(msg, seckey, uid, sessionId, counter, protocol);

        CustomerInfo customer = ApplicationInfo.customerDetails.get(uid);

        out.print(customer.getMessage());
        //System.out.println("msgDecoded -----> : "+msg);

    }

帮帮我...我不需要每次都收到警报，除了我正在关闭浏览窗口...

Answer 1

解决办法是，

我在java脚本中为事件使用锚定标记，而不是按钮。所以“window.onbeforeunload”将事件视为一个新地址。现在我把锚定标签改成了按钮，效果很好。。

Answer 2

执行以下操作之一时，会触发事件onbeforeunload。

Close the current window.
Navigate to another location by entering a new address or selecting a Favorite.
Click an anchor that refers to another document.
Invoke the anchor.click method.
Invoke the document.write method.
Invoke the document.close method.
Invoke the window.close method.
Invoke the window.navigate or NavigateAndFind method.
Invoke the location.replace method.
Invoke the location.reload method.
Specify a new value for the location.href property.
Submit a form to the address specified in the ACTION attribute via the INPUT type=submit control, or invoke the form.submit method.
Invoke the window.open method, providing the possible value _self for the window name.
Invoke the document.open method.
Click the Back, Forward, Refresh, or Home button.

onbeforeunload的MSDN描述