ESB Message Flow

Sample proxy configuration

1. Go inside /samples/axis2Server  and start the simple axis2service :  ./axis2server.sh

2. To send a request to the above proxy, go inside /samples/axis2Client and run the command: ant stockquote -Daddurl=http://localhost:8280/services/TestProxy

So now let's analyze the message In-flow inside ESB.

Message In-Flow

ProxyServiceMessageReceiver is the entry point to Synapse.

Once a message is sent to a proxy service deployed in ESB, is will come to the,

org.apache.synapse.core.axis2.ProxyServiceMessageReceiver::receive()
Receive method here gets a org.apache.axis2.context.MessageContext object.

In the Axis2 level, it uses Axis2 MessageContext. In the mediation engine level, that is, in the Synapse level it needs to be converted to SynapseMessageContext. This is done by MessageContextCreatorForAxis2

Inside the org.apache.synapse.core.axis2.MessageContextCreatorForAxis2::getSynapseMessageContext() method it will get the SynapseConfiguration from AxisConfiguration and get the SynapseEnvironment from AxisConfiguration

Message mediation starts thereafter inside the org.apache.synapse.mediators.base.SequenceMediator::mediate() method. Inside this method, following method call will call to AbstractListMediator::mediate() method.

boolean result = super.mediate(synCtx);

Message mediation starts thereafter inside the org.apache.synapse.mediators.base.SequenceMediator::mediate() method. Inside this method, following method call will call to AbstractListMediator::mediate() method.

boolean result = super.mediate(synCtx);

AbstractListMediator::mediate() method iterate through all the mediators in the mediation flow and verify whether there are content aware mediators exist in the mediation flow. If there are any, it will call AbstractListMediator::buildMessage() in order to build the message.

if (sequenceContentAware && mediator.isContentAware() &&
          (!Boolean.TRUE.equals(synCtx.getProperty(PassThroughConstants.MESSAGE_BUILDER_INVOKED)))) {
          buildMessage(synCtx, synLog);
}

Finally when the SequenceMediator::mediate() method returns true to the ProxyMessageReceiver::receive(), it will send the message to the endpoint.

// if inSequence returns true, forward message to endpointif(inSequenceResult) {
    if (proxy.getTargetEndpoint() != null) {
        Endpoint endpoint = synCtx.getEndpoint(proxy.getTargetEndpoint());

        if (endpoint != null) {
            traceOrDebug(traceOn, "Forwarding message to the endpoint : "                + proxy.getTargetEndpoint());
            endpoint.send(synCtx);

        } else {
            handleException("Unable to find the endpoint specified : " +
                proxy.getTargetEndpoint(), synCtx);
        }

    } else if (proxy.getTargetInLineEndpoint() != null) {
        traceOrDebug(traceOn, "Forwarding the message to the anonymous " +
            "endpoint of the proxy service");
        proxy.getTargetInLineEndpoint().send(synCtx);
    }
}

Exit point from the synapse is org.apache.synapse.core.axis2.Axis2FlexibleMEPClient::send() method.

When a response is returned from the backend, ESB needs to send it back to the client. This message flow is called message Out-Flow. Let's analyze the message out-flow.

Message Out-Flow

In the response path, the entry point to Synapse is org.apache.synapse.core.axis2.SynapseCallbackReceiver::receive() method.

Inside this method, org.apache.synapse.core.axis2.SynapseCallbackReceiver::handleMessage() is called. This method will handle the response or error.

This will call
synapseOutMsgCtx.getEnvironment().injectMessage(synapseInMessageContext);
which will send the response message through the synapse mediation flow.