网上查了多种方法，有不少说法，报400说是传的数据格式不对，最后的结论确实是数据格式不对。
Content_Type为：application/json，配的数据格式有些麻烦，特别数多层，单层还好。
例如，我本传的数据是这个的json：
{
"key1": {
"key11": "value11",
"key12": "value12"
},
"key2": "value2"
}
这时候，postData应该为：{"key1": {\"key11\": \"value11\",\"key12\": \"value12\"},"key2": "value2"}
c#里赋值写法为：
string _postData = "{\"key1\": \"{\\\"key11\\\": \\\"value11\\\",\\\"key12\\\": \\\"value12\\\"}\",\"key2\": \"value2\"}";
post的方法：
protected string PostUrl(string url, string postData)
{
try
{
HttpWebRequest webrequest = (HttpWebRequest)HttpWebRequest.Create(url);
webrequest.Method = "post";
webrequest.ContentType = "application/json;charset=utf-8";
byte[] postdatabyte = Encoding.UTF8.GetBytes(postData);
webrequest.ContentLength = postdatabyte.Length;
Stream stream;
stream = webrequest.GetRequestStream();
stream.Write(postdatabyte, , postdatabyte.Length);
stream.Close();
using (var httpWebResponse = webrequest.GetResponse())
using (StreamReader responseStream = new StreamReader(httpWebResponse.GetResponseStream()))
{
String ret = responseStream.ReadToEnd();
string result = ret.ToString();
return result;
}
}
catch (Exception ex)
{
HttpContext.Current.Response.Write(ex);
return "";
}
}
如果posData的格式写错，运行后报错(using (var httpWebResponse = webrequest.GetResponse()))：System.Net.WebException: 远程服务器返回错误: (400) 错误的请求。 在 System.Net.HttpWebRequest.GetResponse() 。