一直以來，我們都為動態呼叫WebService方法而煩惱。在.Net環境下，最常用的方法就是採用代理類來呼叫WebService，可以通過改變代理類的Url屬性來實現動態呼叫，但當xmlns改變時就會出錯，似乎要重新繫結Webservice並重新編譯後才能再次執行。我無意中通過百度搜索找了一個採用GET/POST/SOAP方式動態呼叫WebService的簡易靈活方法，只需傳入WebService地址、需呼叫的方法及其引數，就可以隨時動態呼叫了。經過測試呼叫成功，現分享給大家，程式碼如下：

using System;
using System.Web;
using System.Xml;
using System.Collections;
using System.Net;
using System.Text;
using System.IO;
using System.Xml.Serialization;

//By huangz 2008-3-19

/**//// <summary>
///  利用WebRequest/WebResponse進行WebService呼叫的類,By 同濟黃正 http://hz932.ys168.com 2008-3-19
/// </summary>
public class WebSvcCaller
{
    //<webServices>
    //  <protocols>
    //    <add name="HttpGet"/>
    //    <add name="HttpPost"/>
    //  </protocols>
    //</webServices>

    private static Hashtable _xmlNamespaces = new Hashtable();//快取xmlNamespace，避免重複呼叫GetNamespace

    /**//// <summary>
    /// 需要WebService支援Post呼叫
    /// </summary>
    public static XmlDocument QueryPostWebService(String URL , String MethodName , Hashtable Pars)
    {
        HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(URL + "/" + MethodName);
        request.Method = "POST";
        request.ContentType = "application/x-www-form-urlencoded";
        SetWebRequest(request);
        byte[] data = EncodePars(Pars);
        WriteRequestData(request , data);

        return ReadXmlResponse(request.GetResponse());
    }
    /**//// <summary>
    /// 需要WebService支援Get呼叫
    /// </summary>
    public static XmlDocument QueryGetWebService(String URL , String MethodName , Hashtable Pars)
    {
        HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(URL + "/" + MethodName + "?" + ParsToString(Pars));
        request.Method = "GET";
        request.ContentType = "application/x-www-form-urlencoded";
        SetWebRequest(request);
        return ReadXmlResponse(request.GetResponse());
    }

    /**//// <summary>
    /// 通用WebService呼叫(Soap),引數Pars為String型別的引數名、引數值
    /// </summary>
    public static XmlDocument QuerySoapWebService(String URL , String MethodName , Hashtable Pars)
    {
        if (_xmlNamespaces.ContainsKey(URL))
        {
            return QuerySoapWebService(URL , MethodName , Pars , _xmlNamespaces[URL].ToString());
        }
        else
        {
            return QuerySoapWebService(URL , MethodName , Pars ,GetNamespace(URL));
        }
    }

    private static XmlDocument QuerySoapWebService(String URL , String MethodName , Hashtable Pars , string XmlNs)
    {    //By 同濟黃正 http://hz932.ys168.com 2008-3-19
        _xmlNamespaces[URL] = XmlNs;//加入快取，提高效率
        HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(URL);
        request.Method = "POST";
        request.ContentType = "text/xml; charset=utf-8";
        request.Headers.Add("SOAPAction" , "\"" + XmlNs + (XmlNs.EndsWith("/") ? "" : "/") + MethodName + "\"");
        SetWebRequest(request);
        byte[] data = EncodeParsToSoap(Pars , XmlNs , MethodName);
        WriteRequestData(request , data);
        XmlDocument doc = new XmlDocument() , doc2 = new XmlDocument();
        doc = ReadXmlResponse(request.GetResponse());

        XmlNamespaceManager mgr = new XmlNamespaceManager(doc.NameTable);
        mgr.AddNamespace("soap" , "http://schemas.xmlsoap.org/soap/envelope/");
        String RetXml = doc.SelectSingleNode("//soap:Body/*/*" , mgr).InnerXml;
        doc2.LoadXml("<root>" + RetXml + "</root>");
        AddDelaration(doc2);
        return doc2;
    }
    private static string GetNamespace(String URL)
    {
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(URL + "?WSDL");
        SetWebRequest(request);
        WebResponse response = request.GetResponse();
        StreamReader sr = new StreamReader(response.GetResponseStream() , Encoding.UTF8);
        XmlDocument doc = new XmlDocument();
        doc.LoadXml(sr.ReadToEnd());
        sr.Close();
        return doc.SelectSingleNode("//@targetNamespace").Value;
    }
    private static byte[] EncodeParsToSoap(Hashtable Pars , String XmlNs , String MethodName)
    {
        XmlDocument doc = new XmlDocument();
        doc.LoadXml("<soap:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\"></soap:Envelope>");
        AddDelaration(doc);
        XmlElement soapBody = doc.CreateElement("soap" , "Body" , "http://schemas.xmlsoap.org/soap/envelope/");
        XmlElement soapMethod = doc.CreateElement(MethodName);
        soapMethod.SetAttribute("xmlns" , XmlNs);
        foreach (string k in Pars.Keys)
        {
            XmlElement soapPar = doc.CreateElement(k);
            soapPar.InnerXml  = ObjectToSoapXml(Pars[k]);
            soapMethod.AppendChild(soapPar);
        }
        soapBody.AppendChild(soapMethod);
        doc.DocumentElement.AppendChild(soapBody);
        return Encoding.UTF8.GetBytes(doc.OuterXml);
    }
    private static string ObjectToSoapXml(object o)
    {
        XmlSerializer mySerializer = new XmlSerializer(o.GetType());
        MemoryStream ms=new MemoryStream();
        mySerializer.Serialize(ms,o);
        XmlDocument doc=new XmlDocument();
        doc.LoadXml(Encoding.UTF8.GetString(ms.ToArray()));
        if(doc.DocumentElement !=null)
        {
            return  doc.DocumentElement.InnerXml ;
        }
        else
        {
            return o.ToString();
        }
    }
    private static void SetWebRequest(HttpWebRequest request)
    {
        request.Credentials = CredentialCache.DefaultCredentials;
        request.Timeout = 10000;
    }

    private static void WriteRequestData(HttpWebRequest request , byte[] data)
    {
        request.ContentLength = data.Length;
        Stream writer = request.GetRequestStream();
        writer.Write(data , 0 , data.Length);
        writer.Close();
    }

    private static byte[] EncodePars(Hashtable Pars)
    {
        return Encoding.UTF8.GetBytes(ParsToString(Pars));
    }

    private static String ParsToString(Hashtable Pars)
    {
        StringBuilder sb = new StringBuilder();
        foreach (string k in Pars.Keys)
        {
            if (sb.Length > 0)
            {
                sb.Append("&");
            }
            sb.Append(HttpUtility.UrlEncode(k) + "=" + HttpUtility.UrlEncode(Pars[k].ToString()));
        }
        return sb.ToString();
    }

    private static XmlDocument ReadXmlResponse(WebResponse response)
    {
        StreamReader sr = new StreamReader(response.GetResponseStream() , Encoding.UTF8);
        String retXml = sr.ReadToEnd();
        sr.Close();
        XmlDocument doc = new XmlDocument();
        doc.LoadXml(retXml);
        return doc;
    }

    private static void AddDelaration(XmlDocument doc)
    {
        XmlDeclaration decl = doc.CreateXmlDeclaration("1.0" , "utf-8" , null);
        doc.InsertBefore(decl , doc.DocumentElement);
    }
}

這個類有三個公用的方法：QuerySoapWebService為通用的採用Soap方式呼叫WebService，QueryGetWebService採用GET方式呼叫，QueryPostWebService採用POST方式呼叫，後兩個方法需要WebService伺服器支援相應的呼叫方式。三個方法的引數和返回值相同：URL為Webservice的Url地址(以.asmx結尾的)；MethodName為要呼叫的方法名稱；Pars為引數表，它的Key為引數名稱，Value為要傳遞的引數的值,Value可為任意物件，前提是這個物件可以被xml序列化。注意方法名稱、引數名稱、引數個數必須完全匹配才能正確呼叫。第一次以Soap方式呼叫時，因為需要查詢WSDL獲取xmlns，因此需要時間相對長些，第二次呼叫不用再讀WSDL，直接從快取讀取。這三個方法的返回值均為XmlDocument物件，這個返回的物件可以進行各種靈活的操作。最常用的一個SelectSingleNode方法，可以讓你一步定位到Xml的任何節點，再讀取它的文字或屬性。也可以直接呼叫Save儲存到磁碟。採用Soap方式呼叫時，根結點名稱固定為root。

這個類主要是利用了WebRequest/WebResponse來完成各種網路查詢操作。為了精簡明瞭，這個類中沒有新增錯誤處理，需要在呼叫的地方設定異常捕獲。

下面是一個呼叫例項：

    protected void Page_Load(object sender , EventArgs e)
    {
        try
        {
            Hashtable pars = new Hashtable();
            String Url = "http://www.260dns.cn/Services/Weather.asmx";
            pars["city"] = "上海";
            pars["wdate"]="2008-3-19";
            XmlDocument doc = WebSvcCaller.QuerySoapWebService(Url , "GetWeather" , pars);
            Response.Write(doc.OuterXml);
        }
        catch (Exception ex)
        {
            Response.Write(ex.Message);
        }
    }