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 == 0))
{
StringBuilder buffer = new StringBuilder();
int i = 0;
foreach (string key in parameters.Keys)
{
if (i > 0)
{
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, 0, 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;
}
}