在 .NET 中使用 WEB SERVICE 的CallBacks机制 (4)

测试
WEB SERVICE Callbacks的概念和设计能使用下列位于http://localhost虚拟目录的三个子项目一起测试。测试的概要已经在上述段落中（Web Service Callback部分）说明。所有项目已经加入了跟踪断点，这样我们可以清楚的看到程序运行的过程(http://www.sysinternals.com/)。下面是它们的实现代码：
1. Web Service A
namespace WebServiceA
{
public class ServiceA : System.Web.Services.WebService
{
public ServiceA()
{
//CODEGEN: This call is required by the ASP.NET Web Services Designer
InitializeComponent();
Trace.WriteLine(string.Format("[{0}]ServiceA.ctor", GetHashCode()));
}

#region Component Designer generated code
private void InitializeComponent()
{
}
#endregion

protected override void Dispose( bool disposing )
{
Trace.WriteLine(string.Format("[{0}]ServiceA.Dispose", GetHashCode()));
}

[WebMethod]
public string DoSomeWorkA(int count, string ticket)
{
Trace.WriteLine(string.Format("[{0}]ServiceA.DoSomeWorkA start...",
GetHashCode()));
int startTC = Environment.TickCount;

// current state
Global.state[ticket] = "The job has been started";
string state = ticket;

// location of the source/target web services -
// (hard coded for test purpose only!)
string myWsdlUrl = "http://localhost/WebServiceA/ServiceA.asmx?wsdl";
string targetWsdlUrl = "http://localhost/WebServiceB/ServiceB.asmx?wsdl";

// call the WebService B
WebServiceAccessor wsa = new WebServiceAccessor(targetWsdlUrl);
object esObj = wsa.CreateInstance("ServiceB");
object retval = wsa.Invoke(esObj, "BeginDoSomeWorkB", count,
myWsdlUrl, state, null, null);

// Wait for the call to complete
WebClientAsyncResult ar = retval as WebClientAsyncResult;
ar.AsyncWaitHandle.WaitOne();

// retrieve a result
object result = wsa.Invoke(esObj, "EndDoSomeWorkB", ar);
int durationTC = Environment.TickCount - startTC;
Trace.WriteLine(string.Format("[{0}]ServiceA.DoSomeWorkA done in {1}ms",
GetHashCode(), durationTC));

//
Global.state.Remove(ticket);
return result.ToString();
}

[WebMethod]
public bool CallbackServiceA(string sender, string xmlEventArg)
{
WebServiceEventArgs ea = (WebServiceEventArgs)xmlEventArg;
string msg = string.Format(
"[{0}]ServiceA.CallbackServiceA({1}, [{2},{3},{4}])",
GetHashCode(), sender, ea.name, ea.state, ea.param);

if(Global.state.ContainsKey(ea.state))
{
Global.state[ea.state] = string.Format("{0}, [{1},{2},{3}]",
sender, ea.name, ea.state, ea.param);
Trace.WriteLine(msg);
return true;
}

return false;
}

[WebMethod]
public string AbortWorkA(string ticket)
{
Trace.WriteLine(string.Format("[{0}]ServiceA.AbortWorkA",
GetHashCode()));

if(Global.state.ContainsKey(ticket))
{
Global.state.Remove(ticket);
return string.Format("#{0} aborted.", ticket);
}

return string.Format("#{0} doesn't exist.", ticket);
}

[WebMethod]
public string GetStatusWorkA(string ticket)
{
if(Global.state.ContainsKey(ticket))
{
return string.Format("#{0} status: {1}", ticket, Global.state[ticket]);
}

return string.Format("#{0} doesn't exist.", ticket);
}
}
}
全局类:
namespace WebServiceA
{
public class Global : System.Web.HttpApplication
{
static public Hashtable state = null;

protected void Application_Start(Object sender, EventArgs e)
{
state = Hashtable.Synchronized(new Hashtable());
Trace.WriteLine(string.Format("[{0}]ServiceA.Application_Start",
GetHashCode()));
}
// ...
protected void Application_End(Object sender, EventArgs e)
{
state.Clear();
Trace.WriteLine(string.Format("[{0}]ServiceA.Application_End",
GetHashCode()));
}
}
}
请求和Callback Web Methods运行在不同的Session 中，这是状态为什么保存在可共享的资源类(如Hashtable)中的原因。每个客户端的请求有一个单独的票据凭证，它是WEB SERVICE和全球站点之间的一把通信钥匙（cookie)。
2. Web Service B
这个网络服务非常简单。 只有一个 Web Methods模拟一些工作。 程序运行期间，服务开始启用Callback Web Methods。工作以同步的方式在运行一些循环操作。每个循环调用WebService”A”的Callback Web Methods，基于它的返回值，程序可以自动停止。Service. 可以在session中保持状态。

namespace WebServiceB
{
public class ServiceB : System.Web.Services.WebService
{
public ServiceB()
{
//CODEGEN: This call is required by the ASP.NET Web Services Designer
InitializeComponent();
Trace.WriteLine(string.Format("[{0}]ServiceB.ctor", GetHashCode()));
}

#region Component Designer generated code
private void InitializeComponent()
{
}
#endregion

protected override void Dispose( bool disposing )
{
Trace.WriteLine(string.Format("[{0}]ServiceB.Dispose", GetHashCode()));
}

[WebMethod(EnableSession=true)]
public string DoSomeWorkB(int count, string callbackWS, string stateWS)
{
Trace.WriteLine(string.Format("[{0}]ServiceB.DoSomeWorkB start...",
GetHashCode()));
int startTC = Environment.TickCount;

// async call to the ServiceA.CallbackServiceA method
WebServiceAccessor wsa = new WebServiceAccessor(callbackWS);
object esObj = wsa.CreateInstance("ServiceA");

// prepare the callback arguments: sender, EventArgs
string sender = GetType().FullName;
WebServiceEventArgs ea = new WebServiceEventArgs();
ea.name = "This is a callback";
ea.state = stateWS;

for(int ii = 0; ii < (count & 0xff); ii++) // max. count = 255
{
ea.param = ii;
string xmlEventArgs = ea;
object retval = wsa.Invoke(esObj, "BeginCallbackServiceA",
sender, xmlEventArgs, null, null);

// simulate some task
Thread.Sleep(250);

// Wait for the call to complete
WebClientAsyncResult ar = retval as WebClientAsyncResult;
ar.AsyncWaitHandle.WaitOne();

// result
object result = wsa.Invoke(esObj, "EndCallbackServiceA", ar);
if((bool)result == false)
{
Trace.WriteLine(string.Format(
"[{0}]ServiceB.DoSomeWorkB has been aborted", GetHashCode()));
return string.Format("#{0} aborted during the progress of {1}.",
stateWS, ii);
}
}
//
int durationTC = Environment.TickCount - startTC;
Trace.WriteLine(string.Format("[{0}]ServiceB.DoSomeWorkB done in {1}ms",
GetHashCode(), durationTC));
return string.Format("#{0} done in {1}ms", stateWS, durationTC);
}
}
}