.Net集成PayPal的Demo

    <form action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post">
        <input type="hidden" name="cmd" value="_cart">
        <input type="hidden" name="upload" value="1">
        <input type="hidden" name="business" value="jacsonwu-facilitator@gmail.com">

        <input type="hidden" name="item_name_1" value="San Francisco Bay(32‘X32‘)">
        <input type="hidden" name="amount_1" value="1.00">
        <input type="hidden" name="quantity_1" value="2">

        <input type="hidden" name="item_name_2" value="Mount Hamilton(24‘x15‘)">
        <input type="hidden" name="amount_2" value="1.00">
        <input type="hidden" name="quantity_2" value="1">

        <input type="hidden" name="currency_code" value="CNY">
　　　　　<!--这里重写url，将覆盖全局设置-->
        <input type="hidden" name="return" value="http://127.0.0.1:56508/ok.aspx">
        <input type="Hidden" name="notify_url" value="http://127.0.0.1:56508/pp.aspx" />

        <input type="submit" value="Upload Cart" alt="Make payments with PayPal-it‘s fastfree and secure!" />
    </form>

string strFormValues = Request.Params.ToString();
            string strNewValue;
            string strResponse;
            string serverURL = "https://www.sandbox.paypal.com/cgi-bin/webscr";

            HttpWebRequest req = (HttpWebRequest)WebRequest.Create(serverURL);
            req.Method = "POST";
            req.ContentType = "application/x-www-form-urlencoded";
            strNewValue = "cmd=_notify-validate";
            strNewValue = "cmd=_notify-synch&tx=" + Request.QueryString["tx"] + "&at=access_token你的";
            //req.ContentLength = strNewValue.Length;

            StreamWriter stOut = new StreamWriter(req.GetRequestStream(), System.Text.Encoding.ASCII);
            stOut.Write(strNewValue);
            stOut.Close();

            StreamReader stIn = new StreamReader(req.GetResponse().GetResponseStream());
            strResponse = stIn.ReadToEnd();
            stIn.Close();
            if (strResponse.StartsWith("SUCCESS"))
            {
            }
            else
            {
            }

//Post back to either sandbox or live
        string strSandbox = "https://www.sandbox.paypal.com/cgi-bin/webscr";
        string strLive = "https://www.paypal.com/cgi-bin/webscr";
        HttpWebRequest req = (HttpWebRequest)WebRequest.Create(strSandbox);

        //Set values for the request back
        req.Method = "POST";
        req.ContentType = "application/x-www-form-urlencoded";
        byte[] param = Request.BinaryRead(HttpContext.Current.Request.ContentLength);
        string strRequest = Encoding.ASCII.GetString(param);
        string ipnPost = strRequest;
        strRequest += "&cmd=_notify-validate";
        req.ContentLength = strRequest.Length;

        //for proxy
        //WebProxy proxy = new WebProxy(new Uri("http://url:port#"));
        //req.Proxy = proxy;

        //Send the request to PayPal and get the response
        StreamWriter streamOut = new StreamWriter(req.GetRequestStream(),
                                 System.Text.Encoding.ASCII);
        streamOut.Write(strRequest);
        streamOut.Close();

        StreamReader streamIn = new StreamReader(req.GetResponse().GetResponseStream());
        string strResponse = streamIn.ReadToEnd();
        streamIn.Close();

        // logging ipn messages... be sure that you give write
        // permission to process executing this code
        string logPathDir = ResolveUrl("");
        string logPath = string.Format("{0}\\{1}.txt",
                         Server.MapPath(logPathDir), DateTime.Now.Ticks);
        File.WriteAllText(logPath, ipnPost + " " + strResponse);
        //

        if (strResponse == "VERIFIED")
        {
            //check the payment_status is Completed
            //check that txn_id has not been previously processed
            //check that receiver_email is your Primary PayPal email
            //check that payment_amount/payment_currency are correct
            //process payment
        }
        else if (strResponse == "INVALID")
        {
            //log for manual investigation
        }
        else
        {
            //log response/ipn data for manual investigation
        }
        Response.Write(strResponse);