Chapter 21. Debugging

21.1. Message Tracing

Message tracing provides a view of the content and context of a message exchange on the SwitchYard bus. Message tracing prints exchange information to the log. An exchange interceptor that generates the trace, is triggered at the following points:
  • Immediately after the consumer sends the request message. For example, In the case of a service which is invoked from a service binding, this is the point at which the gateway binding puts the message onto the bus.
  • Immediately before the service provider is invoked.
  • Immediately after the service provider is invoked.
  • At completion of the exchange before the message is returned to the consumer.

21.1.1. Trace Output Example

Trace output includes details on the metadata, context properties, payload, and attachments for a message exchange. Here is an example of a trace entry:
12:48:25,038 INFO  [org.switchyard.handlers.MessageTraceHandler]
------- Begin Message Trace -------
Consumer -> {urn:switchyard-quickstart:bean-service:0.1.0}OrderService
Provider -> [unassigned]
Operation -> submitOrder
MEP -> IN_OUT
Phase -> IN
State -> OK
Exchange Context ->
    org.switchyard.bus.camel.consumer : ServiceReference [name={urn:switchyard-quickstart:bean-service:0.1.0}OrderService, interface=BaseServiceInterface [type=wsdl, operations=[submitOrder : IN_OUT : [{urn:switchyard-quickstart:bean-service:1.0}submitOrder, {urn:switchyard-quickstart:bean-service:1.0}submitOrderResponse, null]]], domain=ServiceDomain [name=org.switchyard.domains.root]]
    org.switchyard.exchangeGatewayName : _OrderService_soap_1
    org.switchyard.bus.camel.securityContext : SecurityContext[credentials=[ConfidentialityCredential [confidential=false]], securityDomainsToSubjects={}]
    org.switchyard.exchangeInitiatedNS : 1375980505021790000
    CamelCreatedTimestamp : Thu Aug 08 12:48:25 EDT 2013
    org.switchyard.bus.camel.phase : IN
    org.switchyard.bus.camel.dispatcher : org.switchyard.bus.camel.ExchangeDispatcher@b4aa453
    org.switchyard.bus.camel.labels : {org.switchyard.exchangeGatewayName=[org.switchyard.label.behavior.transient]}
    CamelToEndpoint : direct://%7Burn:switchyard-quickstart:bean-service:0.1.0%7DOrderService
    org.switchyard.bus.camel.contract : org.switchyard.metadata.BaseExchangeContract@2176feaf
    org.switchyard.bus.camel.replyHandler : org.switchyard.component.common.SynchronousInOutHandler@516a4aef
    CamelFilterMatched : false
Message Context ->
    org.switchyard.bus.camel.labels : {org.switchyard.contentType=[org.switchyard.label.behavior.transient], org.switchyard.bus.camel.messageSent=[org.switchyard.label.behavior.transient]}
    org.switchyard.messageId : ID-kookaburra-local-49858-1375980502093-0-1
    org.switchyard.bus.camel.messageSent : true
    org.switchyard.soap.messageName : submitOrder
    org.switchyard.contentType : {urn:switchyard-quickstart:bean-service:1.0}submitOrder
    breadcrumbId : ID-kookaburra-local-49858-1375980502093-0-1
Message Content ->
<?xml version="1.0" encoding="UTF-8"?><orders:submitOrder xmlns:orders="urn:switchyard-quickstart:bean-service:1.0">
            <order>
                <orderId>PO-19838-XYZ</orderId>
                <itemId>BUTTER</itemId>
                <quantity>200</quantity>
            </order>
        </orders:submitOrder>
------ End Message Trace -------

21.1.2. Enabling Message Tracing

You can enable message tracing within JBoss Developer Studio.
  • When using the SwitchYard visual editor to view the switchyard.xml file, select the Domain tab to view the Domain Settings, then select the Enable Message Trace check box.
This sets the value of the org.switchyard.handlers.messageTrace.enabled property to true in your application domain. This is captured by the <sy:domain> element in the switchyard.xml source file.

21.2. Exchange Interceptors

Exchange Interceptors provide a mechanism for injecting logic into the message path of the SwitchYard exchange bus. You can use an interceptor to read or update message content and context properties, which makes interceptors useful for debugging and for applying logic outside a traditional service implementation in SwitchYard.

21.2.1. Implementing an Exchange Interceptor

The Java class ExchangeInterceptor has the following properties:
  • Implements the org.switchyard.ExchangeInterceptor interface.
  • Is annotated with @Named so that it can be discovered as a CDI bean.
The ExchangeInterceptor interface looks like this:
public interface ExchangeInterceptor {
    String CONSUMER = "Consumer";
    String PROVIDER = "Provider";
 
    void before(String target, Exchange exchange) throws HandlerException;
    void after(String target, Exchange exchange) throws HandlerException;
    List<String> getTargets();
}
An interceptor is invoked for all message exchanges in an application, so if you only care about a specific service you will want to add a conditional to before() and after() to check for service name. You can restrict the interception points used through the getTargets() method. The CONSUMER and PROVIDER string constants are provided for use with getTargets() to restrict interception to the consumer, provider, or both. The CONSUMER target maps to an injection point just after the consumer sends a request and just before the reply is handed back. The PROVIDER target maps to an injection point just before the provider is called with a request and just after it produces a response.
Here is an example ExchangeInterceptor implementation from the bean-service quickstart:
package org.switchyard.quickstarts.bean.service;
 
import java.util.Arrays;
import java.util.List;
 
import javax.inject.Named;
 
import org.switchyard.Exchange;
import org.switchyard.ExchangeInterceptor;
import org.switchyard.ExchangeState;
import org.switchyard.HandlerException;
 
/**
 * This is an example of an exchange interceptor which can be used to inject code
 * around targets during a message exchange.  This example updates the content of
 * OrderAck after the provider has generated a response.
 */
@Named("UpdateStatus")
public class OrderInterceptor implements ExchangeInterceptor {
 
    @Override
    public void before(String target, Exchange exchange) throws HandlerException {
        // Not interested in doing anything before the provider is invoked
    }
 
    @Override
    public void after(String target, Exchange exchange) throws HandlerException {
        // We only want to intercept successful replies from OrderService
        if (exchange.getProvider().getName().getLocalPart().equals("OrderService")
                && ExchangeState.OK.equals(exchange.getState())) {
            OrderAck orderAck = exchange.getMessage().getContent(OrderAck.class);
            orderAck.setStatus(orderAck.getStatus() + " [intercepted]");
        }
    }
 
    @Override
    public List<String> getTargets() {
       return Arrays.asList(PROVIDER);
    }
 
}