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| |
| <h1>How to Write Your Own Axis2 Transport</h1> |
| |
| <div class="section"><h2>Prologue<a name="Prologue"></a></h2> |
| |
| <p>To stop you from re-inventing the wheel, before we get started, I will |
| quickly list the transports that are already supported in Axis2 with a small |
| description.</p> |
| |
| <p></p> |
| <ul> |
| <li><b>HTTP</b> - In the HTTP transport, the transport Listener is either a |
| Servlet or a Simple HTTP server provided by Axis2. The transport Sender |
| uses sockets to connect and send the SOAP message. Currently we have the |
| commons-httpclient based HTTP Transport sender as the default |
| transport.</li> |
| <li><b>TCP</b> - This is the most simple transport, but needs Addressing |
| support to be functional.</li> |
| </ul> |
| |
| <p>To understand the rest of this document you will need some understanding |
| of the architecture of Axis2. If you are not familiar with the Axis2 |
| architecture, please go through the <a href="Axis2ArchitectureGuide.html">Axis2 Architecture Guide</a> before you |
| read any further.</p> |
| |
| <div class="section"><h2>Introduction<a name="Introduction"></a></h2> |
| |
| <p>Broadly speaking, a transport inside Axis2 can be classified as a way of |
| getting messages that arrive though some channel into the Axis2 engine. The |
| core of Axis2 is transport independent. All data that is transport specific |
| is stripped out of the incoming message and inserted into the MessageContext. |
| In the outgoing message, all transport specific information, like headers, |
| are added and sent.</p> |
| |
| <p>To write your own transport, you will primarily need to write two classes: |
| one is the TransportSender and the other is the TransportReceiver. To |
| register a transport with Axis2 you will need to put entries corresponding |
| to these two classes in the axis2.xml file. I will take you through the |
| process of adding the entries in the relevant sections.</p> |
| |
| <div class="section"><h2>Transport Receiver<a name="Transport_Receiver"></a></h2> |
| |
| <p>Any message that is coming into Axis2 needs to go through a transport |
| receiver. All information about how the message is received at the Axis2 |
| server from the wire (or via an e-mail) is isolated inside the transport |
| receiver. It extracts the data that is coming on the wire and transforms it |
| into a state that the Axis2 server understands.</p> |
| |
| <p>So now that we have some background information about how transports work |
| inside Axis2, without further delay, lets dive into some coding and start |
| building our own transport.</p> |
| |
| <p></p> |
| |
| <p>To get things stared, you will first need to extend from the |
| org.apache.Axis2.transport.TransportListener class and write your own |
| transport listener. To create an engine to process the MessageContext, we |
| need a configuration context. The following code fragment will do this. This |
| should ideally be only done once for the lifetime of the Transport |
| receiver.</p> |
| |
| <p></p> |
| <div><pre>try { |
| //Create a factory |
| ConfigurationContextFactory factory = new ConfigurationContextFactory(); |
| //Use the factory and an Axis2 repository to create a new Configuration Context |
| configurationContext = ConfigurationContextFactory.createConfigurationContextFromFileSystem(repository_directory, |
| axis2xmllocation); |
| } catch (Exception e) { |
| log.info(e.getMessage()); |
| }</pre></div> |
| <p>Now we need some kind of a Listener to listen to the requests that come |
| in. You need to implement this according to the transport that you are trying |
| to build. After a message is received at the Receiver, you can use the |
| following code to process the request and then forward the message context to |
| the engine using the engine.receive(msgContext) method. (The following code |
| is extracted from the MailListener as an example)</p> |
| <div><pre>AxisEngine engine = new AxisEngine(configurationContext); |
| MessageContext msgContext = null; |
| |
| // create and initialize a message context |
| try { |
| TransportInDescription transportIn = |
| reg.getAxisConfiguration().getTransportIn(new QName(Constants.TRANSPORT_NAME)); |
| TransportOutDescription transportOut = |
| reg.getAxisConfiguration().getTransportOut(new QName(Constants.TRANSPORT_NAME)); |
| if (transportIn != null && transportOut != null) { |
| //create Message Context |
| |
| msgContext = new MessageContext(configurationContext, transportIn, transportOut); |
| msgContext.setServerSide(true); |
| msgContext.setProperty(MailSrvConstants.CONTENT_TYPE, message.getContentType()); |
| msgContext.setProperty(MessageContext.CHARACTER_SET_ENCODING, message.getEncoding()); |
| |
| String soapAction = message.getSOAPActionHeader(); |
| msgContext.setWSAAction(soapAction); |
| msgContext.setSoapAction(soapAction); |
| |
| // Here we are trying to set the reply to if it is present in the transport information. |
| msgContext.setReplyTo(new EndpointReference(message.getReplyTo()); |
| |
| //Create the SOAP Message -- This code in from the mail transport and will change depending |
| //on how the data is handled in each transport. |
| ByteArrayInputStream bais = new ByteArrayInputStream(message.getContent().toString().getBytes()); |
| XMLStreamReader reader = XMLInputFactory.newInstance().createXMLStreamReader(bais); |
| |
| String soapNamespaceURI = ""; |
| if(message.getContentType().indexOf(SOAP12Constants.SOAP_12_CONTENT_TYPE) > -1){ |
| soapNamespaceURI = SOAP12Constants.SOAP_ENVELOPE_NAMESPACE_URI; |
| }else if(message.getContentType().indexOf(SOAP11Constants.SOAP_11_CONTENT_TYPE) > -1){ |
| soapNamespaceURI = SOAP11Constants.SOAP_ENVELOPE_NAMESPACE_URI; |
| } |
| |
| StAXBuilder builder = new StAXSOAPModelBuilder(reader, soapNamespaceURI); |
| |
| SOAPEnvelope envelope = (SOAPEnvelope) builder.getDocumentElement(); |
| msgContext.setEnvelope(envelope); |
| engine.receive(msgContext); |
| } else { |
| throw new AxisFault(Messages.getMessage("unknownTransport",Constants.TRANSPORT_NAME)); |
| } |
| |
| } catch (Exception e) { |
| try { |
| if (msgContext != null) { |
| MessageContext faultContext = engine.createFaultMessageContext(msgContext, e); |
| engine.sendFault(faultContext); |
| } else { |
| log.error(e); |
| } |
| } catch (AxisFault e1) { |
| log.error(e); |
| } |
| }</pre></div> |
| <p>Now that we have the coding in place, we need to let Axis2 know about our |
| new transport receiver. We do this by adding an entry into the axis2.xml |
| file. If you need to pass any properties for the transport to operate, it can |
| also be done through the axis2.xml file.</p> |
| <div><pre> <transportReceiver name="TRANSPORT_NAME" class="org.apache.Axis2.transport.TRANSPORT_NAME.TRANSPORT_LISTNER_CLASS"> |
| <parameter name="PROPERTY_NAME">PROPERTY_VALUE</parameter> |
| <parameter name="PROPERTY_NAME_2">PROPERTY_VALUE_2</parameter> |
| </transportReceiver> |
| </pre></div> |
| <p>By using a code fragment like |
| <tt>Utils.getParameterValue(transportOut.getParameter(MailSrvConstants.SMTP_USER))</tt> |
| we can extract the parameters that we inserted into the axis2.xml file.</p> |
| |
| <p>As you can see, getting a new transport receiver up and running is a task |
| that requires very little effort.</p> |
| |
| <div class="section"><h2>Transport Sender<a name="Transport_Sender"></a></h2> |
| |
| <p>Any message that is to be sent out of Axis2, is sent through the Transport |
| Sender. The Transport Sender needs to be extended from the |
| org.apache.Axis2.transport.AbstractTransportSender class.</p> |
| |
| <p>The following bit of code from the abstract transport sender will call the |
| Transport Sender that you wrote.</p> |
| <div><pre>// If an EPR is present then the message is going on a different channel. |
| if (epr != null) { |
| out = openTheConnection(epr, msgContext); |
| OutputStream newOut = startSendWithToAddress(msgContext, out); |
| if (newOut != null) { |
| out = newOut; |
| } |
| writeMessage(msgContext, out); |
| finalizeSendWithToAddress(msgContext, out); |
| } else { |
| out = (OutputStream) msgContext.getProperty(MessageContext.TRANSPORT_OUT); |
| if (out != null) { |
| startSendWithOutputStreamFromIncomingConnection(msgContext, out); |
| writeMessage(msgContext, out); |
| finalizeSendWithOutputStreamFromIncomingConnection(msgContext, out); |
| } else { |
| throw new AxisFault( |
| "Both the TO and Property MessageContext.TRANSPORT_WRITER is Null, No way to send response."); |
| } |
| }</pre></div> |
| <p>Therefore, depending on whether your transport is using the same channel |
| to send the response or using a different channel, you will need to implement |
| a sub-set of the methods from the abstract class.</p> |
| |
| <p>After implementing the necessary methods, you can let Axis2 know about |
| your new transport sender by adding an entry to the axis2.xml file, like you |
| did for the TransportReceiver.</p> |
| <div><pre> <transportSender name="TRANSPORT_NAME" class="org.apache.Axis2.transport.TRANSPORT_NAME.TRANSPORT_SENDER_CLASS"> |
| <parameter name="PROPERTY_NAME">PROPERTY_VALUE</parameter> |
| <parameter name="PROPERTY_NAME_2">PROPERTY_VALUE_2</parameter> |
| </transportSender> |
| </pre></div> |
| <p>Have a look at |
| org.apache.Axis2.transport.http.CommonsHTTPTransportSender which is used to |
| send HTTP responses.</p> |
| |
| <p>Once we have written our transport receiver and our transport sender, and |
| inserted the required entries into the axis2.xml file, we are done. It is as |
| simple as that!</p> |
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