WebClient以POST方式发送Web请求

本例使用WebClient以POST方式发送Web请求并下载一个文件，难点是postData的构造，发送Web请求时有的网站要求可能要求 Cookies前后一致。其中application/x-www-form-urlencoded会告诉服务器该参数是以param1=value1& amp;param2=value2&param3=value3方式拼接的。

private bool postDataandDownloadFile(string fileName)

{

    string url = "http://www.huiyaosoft.com/test.aspx";

    StringBuilder postData = new StringBuilder();

    postData.AppendFormat("{0}={1}&", "username", "admin");

    postData.AppendFormat("{0}={1}&", "password", "");

    postData.AppendFormat("{0}={1}&", "nickname", UrlEncode("辉耀"));

    try

    {

        if (wc == null)

            wc = new System.Net.WebClient();

        wc.Headers.Add("Content-Type", "application/x-www-form-urlencoded");

        wc.Headers.Add("User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko");

        // 继承Cookies

        if (!string.IsNullOrEmpty(cookies))

            wc.Headers.Add("Cookie", cookies);

        // Upload the input string using the HTTP 1.0 POST method.

        byte[] byteArray = System.Text.Encoding.ASCII.GetBytes(postData.ToString());

        // 此处返回的是一个文件

        byte[] byteResult = wc.UploadData(url, "POST", byteArray);

        // 取得Cookies

        cookies = wc.ResponseHeaders["Set-Cookie"];

        if (type ==  || type == )

            writeFile(byteResult, fileName);

    }

    catch (Exception ex)

    {

        MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);

    }

    return false;

}  

由于设置了"Content-Type"为"application/x-www-form-urlencoded"，所以postData必须先进行urlencode。UrlEncode()的作用是将参数进行编码。

public string UrlEncode(string str)

{

    byte[] byStr = System.Text.Encoding.UTF8.GetBytes(str);

    return System.Web.HttpUtility.UrlEncode(byStr);

}

将返回的数据写入文件

//写byte[]到fileName

private bool writeFile(byte[] pReadByte, string fileName)

{

    FileStream pFileStream = null;

    try

    {

        pFileStream = new FileStream(fileName, FileMode.OpenOrCreate);

        pFileStream.Write(pReadByte, , pReadByte.Length);

    }

    catch

    {

        return false;

    }

    finally

    {

        if (pFileStream != null)

            pFileStream.Close();

    }

    return true;

}

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