quinta-feira, 24 de novembro de 2011

How to Reply to a Different JBoss ESB Service

Assume that you have service S1 that cannot have the reply you need ready. Only service S2, which is invoked later by someone else, has the reply you need for service S1.

A very simple case where you may need this, but that you can solve differently: S1 starts a jBPM process orchestrator that does some actions and you want the client invoking S1 to block until the orchestrator has the results ready. Since S1 will not wait until the orchestrator finishes, you need the  orchestrator to call some service S2 to submit the results and somehow S2 should send the results back to the S1 client. In this case you can use the replyToOriginator tag in the ESBNotifier (see the Services Guide). Nevertheless, the following will also work.


Consider the other example I wrote here: Services with one-way requests (without reply) & how to reply later. You can see a couple of lines in the end that are supposed to send a message to the target you want:

LogicalEPR lepr = new LogicalEPR(message.getHeader().getCall().getReplyTo());
ServiceInvoker si = lepr.getServiceInvoker();
si.deliverAsync(message);

Unfortunately this solution will not work in all cases. The problem is in the address we get in the getReplyTo(). In the previous case this was a Logical End-Point, more precisely, the reply-to of the message pointed to the JBpmCallbackService. What if the reply-to address is a physical (?) end-point, say a queue? The previous three lines will simply not work (the first one will throw an exception).

To set the problem, let us see the following jboss-esb.xml.


<?xml version="1.0"?>

<jbossesb parameterReloadSecs="5"
xmlns="http://anonsvn.labs.jboss.com/labs/jbossesb/trunk/product/etc/schemas/xml/jbossesb-1.3.0.xsd"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://anonsvn.labs.jboss.com/labs/jbossesb/trunk/product/etc/schemas/xml/jbossesb-1.3.0.xsd http://anonsvn.jboss.org/repos/labs/labs/jbossesb/trunk/product/etc/schemas/xml/jbossesb-1.3.0.xsd">
<providers>
<jms-provider connection-factory="ConnectionFactory"
name="JMS">
<jms-bus busid="ReplyLaterGWChannel">
<jms-message-filter dest-name="queue/reply_later_Request_gw"
dest-type="QUEUE" />
</jms-bus>
<jms-bus busid="ReplyLaterEsbChannel">
<jms-message-filter dest-name="queue/reply_later_Request_esb"
dest-type="QUEUE" />
</jms-bus>
<jms-bus busid="ReplyLaterEsbChannel2">
<jms-message-filter dest-name="queue/reply_later_Request_esb2"
dest-type="QUEUE" />
</jms-bus>
</jms-provider>
</providers>
<services>
<service category="My_ReplyLater_Service"
description="Reply Late Service: Use this service to invoke the hello"
name="Hello">
<listeners>
<jms-listener busidref="ReplyLaterGWChannel"
is-gateway="true" name="JMS-Gateway" />
<jms-listener busidref="ReplyLaterEsbChannel" name="ESB-Listener" />
</listeners>
<actions mep="OneWay">
<action class="actions.MyListenerAction" name="helloaction"
process="hello" />
<action class="org.jboss.soa.esb.actions.SystemPrintln" name="printMessage">
<property name="message" value="JMS Secured Quickstart message" />
<property name="printfull" value="true" />
</action>

<action name="routeAction" class="org.jboss.soa.esb.actions.StaticRouter">
<property name="destinations">
<route-to destination-name="other-hello"
service-category="My_ReplyLater_Service" service-name="Hello2" />
</property>
</action>

<action class="actions.MyListenerAction" name="helloaction2"
process="hello2" />
</actions>
</service>
<service category="My_ReplyLater_Service"
description="Reply Late Service: Use this service to invoke the hello"
name="Hello2">
<listeners>
<jms-listener busidref="ReplyLaterEsbChannel2" name="ESB-Listener2" />
</listeners>
<actions mep="OneWay">
<action class="actions.MyListenerAction" name="helloaction3"
process="hello3" />
<action class="org.jboss.soa.esb.actions.SystemPrintln" name="printMessage">
<property name="message" value="JMS Secured Quickstart message" />
<property name="printfull" value="true" />
</action>
</actions>
</service>
</services>
</jbossesb>

We have two services:

  • My_ReplyLater_Service/Hello, has an helloaction to begin, a helloaction2 to finish (you will see that the service will never reach helloaction2) and prints the message in the middle, before routing it to  
  • My_ReplyLater_Service/Hello2. The My_ReplyLater_Service/Hello2 invokes helloaction3 and prints the message. 

A crucial point here is that both services are OneWay, i.e., they do not return results to their callers. In this demonstration, the client will invoke My_ReplyLater_Service/Hello synchronously, but will never get a reply, because the service is OneWay. Instead we will "manually" send the reply in the helloaction3, which belongs to a different service.


package actions;


import org.jboss.soa.esb.actions.AbstractActionLifecycle;
import org.jboss.soa.esb.addressing.EPR;
import org.jboss.soa.esb.addressing.MalformedEPRException;
import org.jboss.soa.esb.couriers.Courier;
import org.jboss.soa.esb.couriers.CourierException;
import org.jboss.soa.esb.couriers.CourierFactory;
import org.jboss.soa.esb.helpers.ConfigTree;
import org.jboss.soa.esb.message.Message;

public class MyListenerAction extends AbstractActionLifecycle
{

protected ConfigTree _config;

public MyListenerAction(ConfigTree config) {
_config = config; 

public Message hello(Message message) {
System.out.println("---------------------------------- hello ----------------------------------");
//String xmlEPR = EPRHelper.toXMLString(message.getHeader().getCall().getReplyTo());
//message.getBody().add("replyToAddress", xmlEPR);
System.out.println("-------------------------------- end hello --------------------------------");
return message;
}

public Message hello2(Message message) {
System.out.println("---------------------------------- hello 2 ----------------------------------");
System.out.println("-------------------------------- end hello 2 --------------------------------");
return null;
}

public Message hello3(Message message) throws CourierException, MalformedEPRException {
System.out.println("---------------------------------- hello 3 ----------------------------------");
System.out.println(message);
//String xml = (String) message.getBody().get("replyToAddress");
//EPR jmsepr = (EPR) EPRHelper.fromXMLString(xml);
EPR jmsepr = message.getHeader().getCall().getReplyTo();
message.getHeader().getCall().setTo(jmsepr);

Courier courier = CourierFactory.getCourier(jmsepr);
courier.deliver(message);
courier.cleanup();
System.out.println("-------------------------------- end hello 3 --------------------------------");

return null;
}

}

We get the JMS End-Point Representation from the first service and set the destination of the message using the setTo(). The destination of the message is the client that invoked the My_ReplyLater_Service/Hello service and provided a reply-to field in the message. Note that this is only possible, because this case is somewhat simple and uses only a single message. In other cases, we might need to store and retrieve the reply-to field using some other mechanism. I added in comments the code to do it in a separate body field of the message, using the EPRHelper class (in case the replyTo is changed somewhere).

The Courier class will do the hard work we need, because it accepts Physical EPRs (in fact, the ServiceInvoker also uses it). Unfortunately, the JBoss ESB documentation is very scarce in words about the Courier class. In fact, Courier is an interface. The true class behind this example is JmsCourier. I think that the name says it all: it uses JMS. The courier.cleanup() line will close the JMS MessageProducer (if not closed it may block other MessageProducers that try to write later to the same queue - I saw cases where the service would block without it).


Now, the other files. The deployment.xml:

<?xml version="1.0"?>

<jbossesb-deployment>
  <jmsQueue>reply_later_Request_gw</jmsQueue>
  <jmsQueue>reply_later_Request_esb</jmsQueue>
  <jmsQueue>reply_later_Request_esb2</jmsQueue>
  <jmsQueue>reply_later_Request_esb_reply</jmsQueue>
</jbossesb-deployment>

The jbm-queue-service.xml:


<?xml version="1.0" encoding="UTF-8"?>
<server>

<mbean code="org.jboss.jms.server.destination.QueueService"
name="jboss.esb.quickstart.destination:service=Queue,name=reply_later_Request_gw"
xmbean-dd="xmdesc/Queue-xmbean.xml">
<depends optional-attribute-name="ServerPeer">jboss.messaging:service=ServerPeer
</depends>
</mbean>
<mbean code="org.jboss.jms.server.destination.QueueService"
name="jboss.esb.quickstart.destination:service=Queue,name=reply_later_Request_esb"
xmbean-dd="xmdesc/Queue-xmbean.xml">
<depends optional-attribute-name="ServerPeer">jboss.messaging:service=ServerPeer
</depends>
</mbean>
<mbean code="org.jboss.jms.server.destination.QueueService"
name="jboss.esb.quickstart.destination:service=Queue,name=reply_later_Request_esb2"
xmbean-dd="xmdesc/Queue-xmbean.xml">
<depends optional-attribute-name="ServerPeer">jboss.messaging:service=ServerPeer
</depends>
</mbean>
<mbean code="org.jboss.jms.server.destination.QueueService"
name="jboss.esb.quickstart.destination:service=Queue,name=reply_later_Request_esb_reply"
xmbean-dd="xmdesc/Queue-xmbean.xml">
<depends optional-attribute-name="ServerPeer">jboss.messaging:service=ServerPeer
</depends>
</mbean>
</server>

This is how the ESB project looks like in my JBoss Developer Studio:



Now, to synchronously invoke the Hello service, refer to my other message, and use the following arguments:

My_ReplyLater_Service Hello "my text goes here"

In the end you may want to print the contents of the message like this:

System.out.println("I said: " + reply.getBody().get());

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