在做Web项目时，上传文件是经常会碰到的需求。ASP.Net的WebForm开发模式中，封装了FileUpload控件，可以方便的进行文件上传操作。但有时，你可能不希望使用ASP.Net中的服务器控件，仅仅使用Input标签来实现文件上传。当然也是可以的。下面总结在项目中使用过的上传文件的方式。
一、使用Asp.Net中的FileUpload服务器端控件实现上传
使用asp.net中的服务器端控件FileUpload上传文件非常方便。FileUpload对上传操作进行了封装，你只需要调用SaveAs方法即可完成上传。下面是简单的上传代码。
???<p>服务器端控件上传</p> ???<asp:FileUpload ID="MyFileUpload" runat="server" /> ????????<asp:Button ID="FileUploadButton" runat="server" Text="上传" ????????????onclick="FileUploadButton_Click" />
1 ???protected void FileUploadButton_Click(object sender, EventArgs e) 2 ????????{ 3 ????????????if (MyFileUpload.HasFile) 4 ????????????{ 5 ????????????????string filePath = Server.MapPath("~/UploadFiles/"); 6 ????????????????string fileName = MyFileUpload.PostedFile.FileName; 7 ????????????????MyFileUpload.SaveAs(filePath + fileName); 8 ????????????????Response.Write("<p >上传成功!</p>"); 9 ????????????}10 ????????????else11 ????????????{12 ????????????????Response.Write("<p >请选择要上传的文件!</p>");13 ????????????}14 ????????}当然，在实际项目中就不能这么简单的保存文件了。你至少得增加一些文件类型的判断，防止用户上传一些能够威胁到系统安全的文件。你可以采用客户端JS验证的方式，也能够在.cs的服务器端代码中验证。
在asp.Net WebForm开发框架下，我们也可以利用Html的Input标签来上传文件。这时候需要注意的一点，这个type为file的Input标签需要加上runat="server"属性,否则在后台Request.Files获取不到上传的文件。
?<p>使用Html的Input标签上传</p> ???<input type="file" name="MyFileUploadInput" runat="server" /><asp:Button ????????????ID="InputFileUploadButton" runat="server" Text="上传" ????????????onclick="InputFileUploadButton_Click" />
1 ????????protected void InputFileUploadButton_Click(object sender, EventArgs e) 2 ????????{ 3 ????????????HttpFileCollection files = Request.Files; 4 ????????????string filePath = Server.MapPath("~/UploadFiles/"); 5 ????????????if (files.Count != 0) 6 ????????????{ 7 ????????????????string fileName = files[0].FileName; 8 ????????????????files[0].SaveAs(Path.Combine(filePath, fileName)); 9 ????????????????Response.Write("<p>上传成功</p>");10 ????????????}11 ????????????else12 ????????????{13 ????????????????Response.Write("<p>未获取到Files:"+ files.Count.ToString()+"</p>");14 ????????????}15 ????????}以这种方式进行上传的时候，好处就是可以方便的用JS生成多个Input标签来上传多个文件。且此时需要注意的是，Input标签必须要有name属性。在后台，只需要循环调用SaveAs()方法即可。
接下来的两种上传方式（二和三）都会用到Ajax异步提交数据，后台使用一个.ashx文件进行处理。两种方式共用一个文件，ajax传入的url参数中加一个method来区分哪种方式传过来的。后台代码如下：
1 ???public void ProcessRequest(HttpContext context) 2 ????????{ 3 ????????????string method = context.Request.QueryString["method"].ToString(); 4 ????????????switch (method) 5 ????????????{ 6 ????????????????case "ajaxFileUpload": 7 ????????????????????ajaxFileUpload(context); 8 ????????????????????break; 9 ????????????????case "formDataUpload":10 ????????????????????formDataUpload(context);11 ????????????????????break;12 ????????????????default:13 ????????????????????break;14 ????????????}15 ????????}16 17 ????????private static void formDataUpload(HttpContext context)18 ????????{19 ????????????HttpFileCollection files = context.Request.Files;20 21 ????????????string msg = string.Empty;22 ????????????string error = string.Empty;23 ????????????if (files.Count > 0)24 ????????????{25 ????????????????files[0].SaveAs(ConfigurationManager.AppSettings["FilePath"].ToString() + System.IO.Path.GetFileName(files[0].FileName));26 ????????????????msg = " 成功! 文件大小为:" + files[0].ContentLength;27 ????????????????string res = "{ error:‘" + error + "‘, msg:‘" + msg + "‘}";28 ????????????????context.Response.Write(res);29 ????????????????context.Response.End();30 ????????????}31 ????????}32 33 ????????private static void ajaxFileUpload(HttpContext context)34 ????????{35 ????????????HttpFileCollection files = context.Request.Files;36 37 ????????????string msg = string.Empty;38 ????????????string error = string.Empty;39 ????????????if (files.Count > 0)40 ????????????{41 ????????????????files[0].SaveAs(ConfigurationManager.AppSettings["FilePath"].ToString() + System.IO.Path.GetFileName(files[0].FileName));42 ????????????????msg = " 成功! 文件大小为:" + files[0].ContentLength;43 ????????????????string res = "{ error:‘" + error + "‘, msg:‘" + msg + "‘}";44 ????????????????context.Response.Write(res);45 ????????????????context.Response.End();46 ????????????}47 ????????}二、使用Html中的Input标签加FormData对象实现
使用这种方式上传附件，对浏览器有些要求。FormData属于Html5中新增的特性，IE浏览器只有在10以上才支持。所以，个中利弊自己权衡，但用起来觉得方便。下面直接上代码：
1 ??function formDataUpload() { 2 ????????????var fileupload = document.getElementById(‘fileToUpload‘).files; 3 ????????????var formdata = new FormData(); 4 ????????????formdata.append(‘files‘, fileupload[0]); 5 ????????????var xmlHttp = new XMLHttpRequest(); 6 ????????????xmlHttp.open("post", ‘Handlers/FileUpload.ashx?method=formDataUpload‘); 7 ????????????xmlHttp.onreadystatechange = function () { 8 ????????????????if (xmlHttp.readyState == 4 && xmlHttp.status == 200) { 9 ????????????????????alert(‘上传成功‘);10 ????????????????}11 ????????????}12 ????????????xmlHttp.send(formdata);13 ????????}三、使用Jquery中的ajaxfileupload.js插件实现上传
使用此方法，需要引用jquery.js和ajaxfileupload.js两个文件。还需要注意的部分是两个文件的版本匹配问题，可能在使用过程中会出现些异常。此时发挥搜索引擎的作用，总能找到你需要的解决方案。
JavaScript代码如下：
1 ????function ajaxFileUpLoad() { 2 ????????$.ajaxFileUpload( 3 ????????????{ 4 ????????????????url: ‘Handlers/FileUpload.ashx?method=ajaxFileUpload‘, 5 ????????????????secureuri: false, 6 ????????????????fileElementId: ‘fileToUpload‘, 7 ????????????????dataType: ‘json‘, 8 ????????????????success: function (data, status) { 9 ????????????????????$(‘#img1‘).attr("src", data.imgurl);10 ????????????????????if (typeof (data.error) != ‘undefined‘) {11 ????????????????????????if (data.error != ‘‘) {12 ????????????????????????????alert(data.error);13 ????????????????????????} else {14 ????????????????????????????alert(data.msg);15 ????????????????????????}16 ????????????????????}17 ????????????????},18 ????????????????error: function (data, status, e) {19 ????????????????????alert(e);20 ????????????????}21 ????????????}22 ????????)23 ????????return false;24 ????}Html页面上的代码如下：
1 <html xmlns="http://www.w3.org/1999/xhtml"> 2 <head> 3 <script type="text/javascript" src="Scripts/jquery-1.4.1.js"></script> 4 <script type="text/javascript" src="Scripts/ajaxfileupload.js"></script> 5 <script type="text/javascript"> 6 ????$(function () { 7 ????????$("#ajaxfileuploadButton").click(function () { 8 ????????????ajaxFileUpLoad(); 9 ????????})10 11 ????????$("#formdataButton").click(function () {12 ????????????formDataUpload();13 ????????})14 ????});15 16 </script>17 ????<title></title>18 ????<script type="text/javascript">19 ?????20 ????</script>21 </head>22 <body>23 <input type="file" id="fileToUpload" name="fileToUpload" />24 <input type="button" id="ajaxfileuploadButton" value="ajaxfileupload插件上传" />25 <input type="button" id="formdataButton" value="FormData方式上传" />26 </body>27 </html>ASP.Net上传文件
原文地址：https://www.cnblogs.com/zoujinhua/p/10308866.html