求助:网络问题 HttpWebRequest 和 HttpWebResponse 为什么要定义 static?

请教:
private void button1_Click(object sender, EventArgs e)
{ System.Text.StringBuilder sb = new StringBuilder();
sb.Append("{");

sb.Append("}");
string ret = Utils.WebUtils.postUrl("http://192.168.0.4:8080/emp/2", sb.ToString());
label1.Text = "服务器结果返回：" + ret;
}


public static string postUrl(string url,string body)
{
try
{

var data = body;

string strURL = url;
System.Net.HttpWebRequest request;
request = (System.Net.HttpWebRequest)System.Net.WebRequest.Create(strURL);
request.Method = "POST";
request.ContentType = "application/json;charset=UTF-8";
string paraUrlCoded = data;
byte[] payload;
payload = System.Text.Encoding.UTF8.GetBytes(paraUrlCoded);
request.ContentLength = payload.Length;
Stream writer = request.GetRequestStream();
writer.Write(payload, 0, payload.Length);
writer.Close();


System.Net.HttpWebResponse response;
response = (System.Net.HttpWebResponse)request.GetResponse();
System.IO.Stream s;
s = response.GetResponseStream();

string StrDate = "";
string strValue = "";
StreamReader Reader = new StreamReader(s, Encoding.UTF8);
while ((StrDate = Reader.ReadLine()) != null)
{
strValue += StrDate + "\r\n";
}

return strValue;
}
catch(Exception ex)
{
return "";
}

}


问题1:
public static string postUrl(string url,string body)

为什么要定义 static?

问题2:
sb.Append("{");
sb.Append("}");

这个 {} 有什么用?

问题3:
StreamReader Reader = new StreamReader(s, Encoding.UTF8);
while ((StrDate = Reader.ReadLine()) != null)
{
strValue += StrDate + "\r\n";
}

当下 button1 后

程序会一直等待在这里
吧数据接收完
才会执行后面的程序

是吗？

谢谢！