原理：下载文件时设置一个cookie，客户端利用js间隔性检测cookie，如果检测到则服务端对下载的文件处理完毕，然后通知客户端

http://johnculviner.com/post/2012/03/22/Ajax-like-feature-rich-file-downloads-with-jQuery-File-Download.aspx

下载地址：https://github.com/johnculviner/jquery.fileDownload/blob/master/src/Scripts/jquery.fileDownload.js

/** jQuery File Download Plugin v1.3.3
*
* http://www.johnculviner.com
*
* Copyright (c) 2012 - John Culviner
*
* Licensed under the MIT license:
*   http://www.opensource.org/licenses/mit-license.php*/var $ =jQuery.noConflict();$.extend({//    //$.fileDownload('/path/to/url/', options)//see directly below for possible 'options'fileDownload: function(fileUrl, options) {var defaultFailCallback = function(responseHtml, url) {alert("A file download error has occurred, please try again.");};//provide some reasonable defaults to any unspecified options belowvar settings =$.extend({//            //Requires jQuery UI: provide a message to display to the user when the file download is being prepared before the browser's dialog appears//            preparingMessageHtml: null,//            //Requires jQuery UI: provide a message to display to the user when a file download fails//            failMessageHtml: null,//            //the stock android browser straight up doesn't support file downloads initiated by a non GET: http://code.google.com/p/android/issues/detail?id=1780//specify a message here to display if a user tries with an android browser//if jQuery UI is installed this will be a dialog, otherwise it will be an alert//            androidPostUnsupportedMessageHtml: "Unfortunately your Android browser doesn't support this type of file download. Please try again with a different browser.",//            //Requires jQuery UI: options to pass into jQuery UI Dialog//            dialogOptions: { modal: true},//            //a function to call after a file download dialog/ribbon has appeared//Args://url - the original url attempted//            successCallback: function(url) { },//            //a function to call after a file download dialog/ribbon has appeared//Args://responseHtml    - the html that came back in response to the file download. this won't necessarily come back depending on the browser.//in less than IE9 a cross domain error occurs because 500+ errors cause a cross domain issue due to IE subbing out the//server's error message with a "helpful" IE built in message//url             - the original url attempted//failCallback: defaultFailCallback,//            //the HTTP method to use. Defaults to "GET".//            httpMethod: "GET",//            //if specified will perform a "httpMethod" request to the specified 'fileUrl' using the specified data.//data must be an object (which will be $.param serialized) or already a key=value param string//            data: null,//            //a period in milliseconds to poll to determine if a successful file download has occured or not//            checkInterval: 100,//            //the cookie name to indicate if a file download has occured//            cookieName: "fileDownload",//            //the cookie value for the above name to indicate that a file download has occured//            cookieValue: "true",//            //the cookie path for above name value pair//            cookiePath: "/",//            //the title for the popup second window as a download is processing in the case of a mobile browser//            popupWindowTitle: "Initiating file download...",//            //Functionality to encode HTML entities for a POST, need this if data is an object with properties whose values contains strings with quotation marks.//HTML entity encoding is done by replacing all &,<,>,',",\r,\n characters.//Note that some browsers will POST the string htmlentity-encoded whilst others will decode it before POSTing.//It is recommended that on the server, htmlentity decoding is done irrespective.//            encodeHTMLEntities: true}, options);//Setup mobile browser detection: Partial credit: http://detectmobilebrowser.com/var userAgent = (navigator.userAgent || navigator.vendor ||window.opera).toLowerCase();var isIos = false;                  //has full support of features in iOS 4.0+, uses a new window to accomplish this.var isAndroid = false;              //has full support of GET features in 4.0+ by using a new window. POST will resort to a POST on the current window.var isOtherMobileBrowser = false;   //there is no way to reliably guess here so all other mobile devices will GET and POST to the current window.if (/ip(ad|hone|od)/.test(userAgent)) {isIos= true;}else if (userAgent.indexOf('android') != -1) {isAndroid= true;}else{isOtherMobileBrowser= /avantgo|bada\/|blackberry|blazer|compal|elaine|fennec|hiptop|playbook|silk|iemobile|iris|kindle|lge |maemo|midp|mmp|netfront|opera m(ob|in)i|palm( os)?|phone|p(ixi|re)\/|plucker|pocket|psp|symbian|treo|up\.(browser|link)|vodafone|wap|windows (ce|phone)|xda|xiino/i.test(userAgent) || /1207|6310|6590|3gso|4thp|50[1-6]i|770s|802s|a wa|abac|ac(er|oo|s\-)|ai(ko|rn)|al(av|ca|co)|amoi|an(ex|ny|yw)|aptu|ar(ch|go)|as(te|us)|attw|au(di|\-m|r |s )|avan|be(ck|ll|nq)|bi(lb|rd)|bl(ac|az)|br(e|v)w|bumb|bw\-(n|u)|c55\/|capi|ccwa|cdm\-|cell|chtm|cldc|cmd\-|co(mp|nd)|craw|da(it|ll|ng)|dbte|dc\-s|devi|dica|dmob|do(c|p)o|ds(12|\-d)|el(49|ai)|em(l2|ul)|er(ic|k0)|esl8|ez([4-7]0|os|wa|ze)|fetc|fly(\-|_)|g1 u|g560|gene|gf\-5|g\-mo|go(\.w|od)|gr(ad|un)|haie|hcit|hd\-(m|p|t)|hei\-|hi(pt|ta)|hp( i|ip)|hs\-c|ht(c(\-| |_|a|g|p|s|t)|tp)|hu(aw|tc)|i\-(20|go|ma)|i230|iac( |\-|\/)|ibro|idea|ig01|ikom|im1k|inno|ipaq|iris|ja(t|v)a|jbro|jemu|jigs|kddi|keji|kgt( |\/)|klon|kpt |kwc\-|kyo(c|k)|le(no|xi)|lg( g|\/(k|l|u)|50|54|e\-|e\/|\-[a-w])|libw|lynx|m1\-w|m3ga|m50\/|ma(te|ui|xo)|mc(01|21|ca)|m\-cr|me(di|rc|ri)|mi(o8|oa|ts)|mmef|mo(01|02|bi|de|do|t(\-| |o|v)|zz)|mt(50|p1|v )|mwbp|mywa|n10[0-2]|n20[2-3]|n30(0|2)|n50(0|2|5)|n7(0(0|1)|10)|ne((c|m)\-|on|tf|wf|wg|wt)|nok(6|i)|nzph|o2im|op(ti|wv)|oran|owg1|p800|pan(a|d|t)|pdxg|pg(13|\-([1-8]|c))|phil|pire|pl(ay|uc)|pn\-2|po(ck|rt|se)|prox|psio|pt\-g|qa\-a|qc(07|12|21|32|60|\-[2-7]|i\-)|qtek|r380|r600|raks|rim9|ro(ve|zo)|s55\/|sa(ge|ma|mm|ms|ny|va)|sc(01|h\-|oo|p\-)|sdk\/|se(c(\-|0|1)|47|mc|nd|ri)|sgh\-|shar|sie(\-|m)|sk\-0|sl(45|id)|sm(al|ar|b3|it|t5)|so(ft|ny)|sp(01|h\-|v\-|v )|sy(01|mb)|t2(18|50)|t6(00|10|18)|ta(gt|lk)|tcl\-|tdg\-|tel(i|m)|tim\-|t\-mo|to(pl|sh)|ts(70|m\-|m3|m5)|tx\-9|up(\.b|g1|si)|utst|v400|v750|veri|vi(rg|te)|vk(40|5[0-3]|\-v)|vm40|voda|vulc|vx(52|53|60|61|70|80|81|83|85|98)|w3c(\-| )|webc|whit|wi(g |nc|nw)|wmlb|wonu|x700|xda(\-|2|g)|yas\-|your|zeto|zte\-/i.test(userAgent.substr(0, 4));}var httpMethodUpper =settings.httpMethod.toUpperCase();if (isAndroid && httpMethodUpper != "GET") {//the stock android browser straight up doesn't support file downloads initiated by non GET requests: http://code.google.com/p/android/issues/detail?id=1780if($().dialog) {$("<div>").html(settings.androidPostUnsupportedMessageHtml).dialog(settings.dialogOptions);}else{alert(settings.androidPostUnsupportedMessageHtml);}return;}//wire up a jquery dialog to display the preparing message if specifiedvar $preparingDialog = null;if(settings.preparingMessageHtml) {$preparingDialog= $("<div>").html(settings.preparingMessageHtml).dialog(settings.dialogOptions);}var internalCallbacks ={onSuccess:function(url) {//remove the perparing message if it was specifiedif($preparingDialog) {$preparingDialog.dialog('close');};settings.successCallback(url);},onFail:function(responseHtml, url) {//remove the perparing message if it was specifiedif($preparingDialog) {$preparingDialog.dialog('close');};//wire up a jquery dialog to display the fail message if specifiedif(settings.failMessageHtml) {$("<div>").html(settings.failMessageHtml).dialog(settings.dialogOptions);//only run the fallcallback if the developer specified something different than default//otherwise we would see two messages about how the file download failedif (settings.failCallback !=defaultFailCallback) {settings.failCallback(responseHtml, url);}}else{settings.failCallback(responseHtml, url);}}};//make settings.data a param string if it exists and isn't alreadyif (settings.data !== null && typeof settings.data !== "string") {settings.data=$.param(settings.data);}var$iframe,downloadWindow,formDoc,$form;if (httpMethodUpper === "GET") {if (settings.data !== null) {//need to merge any fileUrl params with the data objectvar qsStart = fileUrl.indexOf('?');if (qsStart != -1) {//we have a querystring in the urlif (fileUrl.substring(fileUrl.length - 1) !== "&") {fileUrl= fileUrl + "&";}}else{fileUrl= fileUrl + "?";}fileUrl= fileUrl +settings.data;}if (isIos ||isAndroid) {downloadWindow=window.open(fileUrl);downloadWindow.document.title=settings.popupWindowTitle;window.focus();}else if(isOtherMobileBrowser) {window.location(fileUrl);}else{//create a temporary iframe that is used to request the fileUrl as a GET request$iframe = $("<iframe>").hide().attr("src", fileUrl).appendTo("body");}}else{var formInnerHtml = "";if (settings.data !== null) {$.each(settings.data.replace(/\+/g, ' ').split("&"), function() {var kvp = this.split("=");var key = settings.encodeHTMLEntities ? htmlSpecialCharsEntityEncode(decodeURIComponent(kvp[0])) : decodeURIComponent(kvp[0]);if (!key) return;var value = kvp[1] || '';value= settings.encodeHTMLEntities ? htmlSpecialCharsEntityEncode(decodeURIComponent(kvp[1])) : decodeURIComponent(kvp[1]);formInnerHtml+= '<input type="hidden" name="' + key + '" value="' + value + '" />';});}if(isOtherMobileBrowser) {$form= $("<form>").appendTo("body");$form.hide().attr('method', settings.httpMethod).attr('action', fileUrl).html(formInnerHtml);}else{if(isIos) {downloadWindow= window.open("about:blank");downloadWindow.document.title=settings.popupWindowTitle;formDoc=downloadWindow.document;window.focus();}else{$iframe= $("<iframe style='display: none' src='about:blank'></iframe>").appendTo("body");formDoc=getiframeDocument($iframe);}formDoc.write("<html><head></head><body><form method='" + settings.httpMethod + "' action='" + fileUrl + "'>" + formInnerHtml + "</form>" + settings.popupWindowTitle + "</body></html>");$form= $(formDoc).find('form');}$form.submit();}//check if the file download has completed every checkInterval ms
setTimeout(checkFileDownloadComplete, settings.checkInterval);functioncheckFileDownloadComplete() {//has the cookie been written due to a file download occuring?if (document.cookie.indexOf(settings.cookieName + "=" + settings.cookieValue) != -1) {//execute specified callback
internalCallbacks.onSuccess(fileUrl);//remove the cookie and iframevar date = new Date(1000);document.cookie= settings.cookieName + "=; expires=" + date.toUTCString() + "; path=" +settings.cookiePath;cleanUp(false);return;}//has an error occured?//if neither containers exist below then the file download is occuring on the current windowif (downloadWindow ||$iframe) {//has an error occured?try{varformDoc;if(downloadWindow) {formDoc=downloadWindow.document;}else{formDoc=getiframeDocument($iframe);}if (formDoc && formDoc.body != null && formDoc.body.innerHTML.length > 0) {var isFailure = true;if ($form && $form.length > 0) {var $contents =$(formDoc.body).contents().first();if ($contents.length > 0 && $contents[0] === $form[0]) {isFailure= false;}}if(isFailure) {internalCallbacks.onFail(formDoc.body.innerHTML, fileUrl);cleanUp(true);return;}}}catch(err) {//500 error less than IE9internalCallbacks.onFail('', fileUrl);cleanUp(true);return;}}//keep checking...
setTimeout(checkFileDownloadComplete, settings.checkInterval);}//gets an iframes document in a cross browser compatible mannerfunctiongetiframeDocument($iframe) {var iframeDoc = $iframe[0].contentWindow || $iframe[0].contentDocument;if(iframeDoc.document) {iframeDoc=iframeDoc.document;}returniframeDoc;}functioncleanUp(isFailure) {setTimeout(function() {if(downloadWindow) {if(isAndroid) {downloadWindow.close();}if(isIos) {if(isFailure) {downloadWindow.focus();//ios safari bug doesn't allow a window to be closed unless it is focused
downloadWindow.close();}else{downloadWindow.focus();}}}},0);}functionhtmlSpecialCharsEntityEncode(str) {return str.replace(/&/gm, '&amp;').replace(/\n/gm, "&#10;").replace(/\r/gm, "&#13;").replace(/</gm, '&lt;').replace(/>/gm, '&gt;').replace(/"/gm, '&quot;').replace(/'/gm, '&apos;'); //single quotes just to be safe
}}
});