本来想用jsonp来跨域请求的，但sb写接口的，不改返回值。。。只得在后台请求接口了。。。

string url = "ssss.com";
//demo里的是get请求
HttpWebResponse w = HttpHelper.CreateGetHttpResponse(url, 30000, null, null);
StreamReader sr = new StreamReader(w.GetResponseStream());
string/*这是Json字符串*/ jsonstr = sr.ReadToEnd();

using System;
using System.Collections.Generic;
using System.IO;
using System.Net;
using System.Net.Security;
using System.Security.Cryptography.X509Certificates;
using System.Text;
public class HttpHelper
{

    /// <summary>
    /// 创建GET方式的HTTP请求
    /// </summary>
    ///
    public static HttpWebResponse CreateGetHttpResponse(string url, int timeout, string userAgent, CookieCollection cookies)
    {
        HttpWebRequest request = null;
        if (url.StartsWith("https", StringComparison.OrdinalIgnoreCase))
        {
            //对服务端证书进行有效性校验（非第三方权威机构颁发的证书，如自己生成的，不进行验证，这里返回true）
            ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(CheckValidationResult);
            request = WebRequest.Create(url) as HttpWebRequest;
            request.ProtocolVersion = HttpVersion.Version10;    //http版本，默认是1.1,这里设置为1.0
        }
        else
        {
            request = WebRequest.Create(url) as HttpWebRequest;
        }
        request.Method = "GET";

        //设置代理UserAgent和超时
        //request.UserAgent = userAgent;
        //request.Timeout = timeout;
        if (cookies != null)
        {
            request.CookieContainer = new CookieContainer();
            request.CookieContainer.Add(cookies);
        }
        return request.GetResponse() as HttpWebResponse;
    }

    /// <summary>
    /// 创建POST方式的HTTP请求
    /// </summary>
    public static HttpWebResponse CreatePostHttpResponse(string url, IDictionary<string, string> parameters, int timeout, string userAgent, CookieCollection cookies)
    {
        HttpWebRequest request = null;
        //如果是发送HTTPS请求
        if (url.StartsWith("https", StringComparison.OrdinalIgnoreCase))
        {
            //ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(CheckValidationResult);
            request = WebRequest.Create(url) as HttpWebRequest;
            //request.ProtocolVersion = HttpVersion.Version10;
        }
        else
        {
            request = WebRequest.Create(url) as HttpWebRequest;
        }
        request.Method = "POST";
        request.ContentType = "application/x-www-form-urlencoded";

        //设置代理UserAgent和超时
        //request.UserAgent = userAgent;
        //request.Timeout = timeout; 

        if (cookies != null)
        {
            request.CookieContainer = new CookieContainer();
            request.CookieContainer.Add(cookies);
        }
        //发送POST数据
        if (!(parameters == null || parameters.Count == ))
        {
            StringBuilder buffer = new StringBuilder();
            int i = ;
            foreach (string key in parameters.Keys)
            {
                if (i > )
                {
                    buffer.AppendFormat("&{0}={1}", key, parameters[key]);
                }
                else
                {
                    buffer.AppendFormat("{0}={1}", key, parameters[key]);
                    i++;
                }
            }
            byte[] data = Encoding.ASCII.GetBytes(buffer.ToString());
            using (Stream stream = request.GetRequestStream())
            {
                stream.Write(data, , data.Length);
            }
        }
        string[] values = request.Headers.GetValues("Content-Type");
        return request.GetResponse() as HttpWebResponse;
    }

    /// <summary>
    /// 获取请求的数据
    /// </summary>
    public static string GetResponseString(HttpWebResponse webresponse)
    {
        using (Stream s = webresponse.GetResponseStream())
        {
            StreamReader reader = new StreamReader(s, Encoding.UTF8);
            return reader.ReadToEnd();

        }
    }

    /// <summary>
    /// 验证证书
    /// </summary>
    private static bool CheckValidationResult(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors)
    {
        if (errors == SslPolicyErrors.None)
            return true;
        return false;
    }
}