.NET SOAP over JMS
Boiled down, this JMS solution hijacks the SOAP request before it goes over the wire, sends it over JMS, listens for a response via JMS then returns the SOAP response back to the caller, allowing it to finish processing. We only pass the SOAP through the system - we don't have to do anything special to generate it, process it, serialize it, or deserialize it. We let .NET do the heavy lifting that it was going to do anyway.

Normally, a Web Service will use an HTTP URI. When the Web Service proxy makes http calls, it causes the WebRequest.Create() method to produce an instance of HttpWebRequest. The proxy generates the SOAP, hands it off to the HttpWebRequest, which sends it over the wire, gets a response, and then sends that to the HttpWebResponse. Finally, the proxy takes over again. (See Figure 2)

We're going to take advantage of the "pluggable protocol" feature in .NET to make using JMS almost transparent. We say "almost" because we don't want to supersede HTTP in all cases - just for certain services. First, we'll need to know what flavor of JMS we're using. For this article, we're focusing on ActiveMQ because it's freely available and already has a pure .NET API. The .NET API we use is from Spring.NET. There are other options, such as OpenMQ and Tibco. Even if there were no .NET APIs already, we could wrap a dll. If the API existed only in Java, there are technologies such as JNBridge that can bridge technologies.

Once the JMS API is selected, we need to create several components: an ActiveMqWebResponse, an ActiveMqWebRequest, an ActiveMqWebRequestCreate, and an ActiveMqSoapStream - a specialized stream for hijacking the SOAP. These classes are custom versions of the components used in the normal flow of HTTP Web Services. Then, of course, we need a consumer.

ActiveMqSoapStream
The specialized stream is where we do the fancy footwork to hijack the SOAP. We don't want the proxy to realize it's dealing with a special stream. This class inherits System.IO.Stream and is mostly a pass-through to an encapsulated stream. The primary difference is that it overrides the Close() method called by the base WebRequest. Instead of closing the stream, this method rewinds the inner stream so our hijacking code can process the stream from the beginning. It also has an internal close method that our ActiveMqWebRequest will call to truly close the underlying stream when it's done with it, otherwise the stream would stay open indefinitely.

public class ActiveMqSoapStream : Stream
{
      private Stream m_Stream;
      public override void Close()
      { m_Stream.Position = 0;}
      internal void InternalClose()
      { if (this.CanSeek == true) m_Stream.Close();}
}

ActiveMqWebRequest
The ActiveMqWebRequest is where the bulk of the work happens. It inherits from System.NET.WebRequest and implements the abstract methods and properties. There are a few custom properties for JMS-specific information such as the address, username, password, and queue name. We also have a field of type ActiveMqSoapStream.

public class ActiveMqQueueWebRequest : WebRequest
{
      protected ActiveMqSoapStream m_RequestStream;
      private string _password;
      private string _username;
      private string _queueAddress;
      private string _queueName;
      ...

For brevity's sake, I won't go into the details of the property accessors or pass-through methods. The methods we're most interested in are GetRequestStream() and Get-Response(). GetRequestStream() is where we replace the default stream with our own.

public override Stream GetRequestStream()
{
    m_RequestStream = new ActiveMqSoapStream(new MemoryStream(),
true, true, true);
    return m_RequestStream;
}

GetResponse() is where we send the request, listen for a response, and then put the response in a return stream. This is the workhorse of the class. The first thing we do is access the SOAP stream as an array of bytes.

public override WebResponse GetResponse()
{
    byte[] bytBody = new Byte[m_RequestStream.Length];
    m_RequestStream.Read(bytBody, 0, bytBody.Length);