c#模拟提交带附件的表单

//工具类
public static class FormUpload
    {
        private static readonly Encoding encoding = Encoding.UTF8;

        public static HttpWebResponse MultipartFormDataPost(string postUrl, string userAgent, Dictionary<string, object> postParameters)
        {
            string formDataBoundary = String.Format("----------{0:N}", Guid.NewGuid());
            string contentType = "multipart/form-data; boundary=" + formDataBoundary;

            byte[] formData = GetMultipartFormData(postParameters, formDataBoundary);

            return PostForm(postUrl, userAgent, contentType, formData);
        }

        private static HttpWebResponse PostForm(string postUrl, string userAgent, string contentType, byte[] formData)
        {
            HttpWebRequest request = WebRequest.Create(postUrl) as HttpWebRequest;

            if (request == null)
            {
                throw new NullReferenceException("request is not a http request");
            }

            // Set up the request properties.
            request.Method = "POST";
            request.ContentType = contentType;
            request.UserAgent = userAgent;
            request.CookieContainer = new CookieContainer();
            request.ContentLength = formData.Length;

            // You could add authentication here as well if needed:
            // request.PreAuthenticate = true;
            // request.AuthenticationLevel = System.Net.Security.AuthenticationLevel.MutualAuthRequested;
            // request.Headers.Add("Authorization", "Basic " + Convert.ToBase64String(System.Text.Encoding.Default.GetBytes("username" + ":" + "password")));

            // Send the form data to the request.
            using (Stream requestStream = request.GetRequestStream())
            {
                requestStream.Write(formData, 0, formData.Length);
                requestStream.Close();
            }

            return request.GetResponse() as HttpWebResponse;
        }

        private static byte[] GetMultipartFormData(Dictionary<string, object> postParameters, string boundary)
        {
            Stream formDataStream = new System.IO.MemoryStream();
            bool needsCLRF = false;

            foreach (var param in postParameters)
            {
                // Thanks to feedback from commenters, add a CRLF to allow multiple parameters to be added.
                // Skip it on the first parameter, add it to subsequent parameters.
                if (needsCLRF)
                    formDataStream.Write(encoding.GetBytes("
"), 0, encoding.GetByteCount("
"));

                needsCLRF = true;

                if (param.Value is FileParameter)
                {
                    FileParameter fileToUpload = (FileParameter)param.Value;

                    // Add just the first part of this param, since we will write the file data directly to the Stream
                    string header = string.Format("--{0}
Content-Disposition: form-data; name="{1}"; filename="{2}";
Content-Type: {3}

",
                        boundary,
                        param.Key,
                        fileToUpload.FileName ?? param.Key,
                        fileToUpload.ContentType ?? "application/octet-stream");

                    formDataStream.Write(encoding.GetBytes(header), 0, encoding.GetByteCount(header));

                    // Write the file data directly to the Stream, rather than serializing it to a string.
                    formDataStream.Write(fileToUpload.File, 0, fileToUpload.File.Length);
                }
                else
                {
                    string postData = string.Format("--{0}
Content-Disposition: form-data; name="{1}"

{2}",
                        boundary,
                        param.Key,
                        param.Value);
                    formDataStream.Write(encoding.GetBytes(postData), 0, encoding.GetByteCount(postData));
                }
            }

            // Add the end of the request.  Start with a newline
            string footer = "
--" + boundary + "--
";
            formDataStream.Write(encoding.GetBytes(footer), 0, encoding.GetByteCount(footer));

            // Dump the Stream into a byte[]
            formDataStream.Position = 0;
            byte[] formData = new byte[formDataStream.Length];
            formDataStream.Read(formData, 0, formData.Length);
            formDataStream.Close();

            return formData;
        }

        public class FileParameter
        {
            public byte[] File { get; set; }
            public string FileName { get; set; }
            public string ContentType { get; set; }
            public FileParameter(byte[] file) : this(file, null) { }
            public FileParameter(byte[] file, string filename) : this(file, filename, null) { }
            public FileParameter(byte[] file, string filename, string contenttype)
            {
                File = file;
                FileName = filename;
                ContentType = contenttype;
            }
        }
    }
//调用

//构造文件
                FormUpload.FileParameter file = new FormUpload.FileParameter(File.ReadAllBytes("D://TestAdvertiserFile.jpg"), "TestAdvertiserFile.jpg");

                //构造参数
                Dictionary<string, object> postParams = new Dictionary<string, object>();
                postParams.Add("demoId", 3);
                postParams.Add("token", "TnQqQSDFSDI#2121231");
                postParams.Add("advertiserId", input.SinaInput.Id);
                postParams.Add("name", input.SinaInput.Name);
                postParams.Add("industry",input.SinaInput.Industry);

                //文件作为参数加入，如果有多个文件，可以参照加入多个
                postParams.Add("qualificationFiles", file);

                //提交请求，获得返回结果
                var httpWebResp = FormUpload.MultipartFormDataPost("http://amp.ad.sina.com.cn/sax/interface/advertiser/upload.action", "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.3 Safari/535.19", postParams);

                Stream instream = httpWebResp.GetResponseStream();
                StreamReader sr = new StreamReader(instream,Encoding.UTF8);
                //返回结果网页(html)代码
                string response = sr.ReadToEnd();
                sr.Close();