Ajax:读取响应首部

   有时,只是想“ping”一下服务器,验证服务器是否正常运行。此时,只需要读取服务器发出的响应首部,而忽略内容。通过读取响应首部,可以得出content-Type(内容类型)、Content-Length(内容长度)。甚至LastModified(最后一次修改)的日期。

<html xmlns="http://www.w3.org/1999/xhtml">

<head>

    <title></title>

    <script type="text/javascript">

        var xmlHttp;

        var requestType = "";

        function createXMLHttpRequest() {

            if (window.ActiveXObject) {

                xmlHttp = new ActiveXObject("Microsoft.XMLHTTp");

            }

            else if (window.XMLHttpRequest) {

                xmlHttp = new XMLHttpRequest();

            }

        }





        function doRequest(request, url) {

            createXMLHttpRequest();

            requestType = request;

            xmlHttp.onreadystatechange = handleStateChange;

            xmlHttp.open("GET", url, true);

            xmlHttp.send(null);

        }

        function handleStateChange() {

            if (xmlHttp.readyState == 4) {



                if (requestType == "allResponseHeaders") {

                    getAllResponseHeaders();

                }

                else if (requestType == "lastModified") {



                    getLastModified();

                }

                else if (requestType == "isResourceAvailable") {

                    getIsResourceAvailable();

                }



            }

        }

        function getAllResponseHeaders() {



            alert(xmlHttp.getAllResponseHeaders());

        }

        function getLastModified() {

            alert("Last Modified:" + xmlHttp.getResponseHeader("Last-Modified"));

        }



        function getIsResourceAvailable() {

            if (xmlHttp.status == 200) {

                alert("Successful response");

            }

            else if (xmlHttp.status == 404) {

                alert("Resource is unavailable");

            }

            else {

                alert("Unexpected response status:" + xmlHttp.status);

            }

        }

    </script>

</head>

<body>

    <h1>

        Reading Response Headers</h1>

    <a href="javascript:doRequest('allResponseHeaders','readingResponseHeaders.xml');">Read

        All Resoponse Headers</a><br />

    <a href="javascript:doRequest('lastModified','readingResponseHeaders.xml');">Get Last

        Modified Date</a><br />

    <a href="javascript:doRequest('isResourceAvailable','readingResponseHeaders.xml');">

        Read Available Resource </a>

    <br />

    <a href="javascript:doRequest('isResourceAvailable','no-available.xml');">Read UnAvailable

        Resource </a>

    <br />

</body>

</html>

readingResponseHeaders.xml文件内容为:

<?xml version="1.0" encoding="utf-8" ?>

<readingResponseHeaders>



</readingResponseHeaders>

执行效果如下:

Ajax:读取响应首部

挨个点击出现效果:

Ajax:读取响应首部

Ajax:读取响应首部

Ajax:读取响应首部

Ajax:读取响应首部

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