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&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", "123456");
    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 == 1 || type == 3)
            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);
}

//写byte[]到fileName  
private bool writeFile(byte[] pReadByte, string fileName)
{
    FileStream pFileStream = null;
    try
    {
        pFileStream = new FileStream(fileName, FileMode.OpenOrCreate);
        pFileStream.Write(pReadByte, 0, pReadByte.Length);
    }
    catch
    {
        return false;
    }
    finally
    {
        if (pFileStream != null)
            pFileStream.Close();
    }
    return true;
}