Tracer

Tracer is the sister to Camel's Debugger. They are much alike.
Camel supports a tracer interceptor that is used for logging the route executions at INFO level.

The Tracer is an InterceptStrategy which can be applied to a DefaultCamelContext or SpringCamelContext to ensure that there is a TracerInterceptor created for every node in the DSL.

Formatting

The tracer formats the execution of exchanges to log lines. They are logged at INFO level in the log category: org.apache.camel.processor.interceptor.TraceInterceptor.
The tracer uses by default TraceFormatter to format the log line.

TraceFormatter has the following options

Option	Default	Description
showBreadCrumb	true	Outputs the unique unit of work for the exchange. To be used for correlation so you can identify the same exchange.
showNode	true	The destination node.
showExchangeId	false	To output the unique exchange id. Currently the breadcrumb is sufficient.
showProperties	true	Output the exchange properties
showHeaders	true	Output the in message headers
showBodyType	true	Output the in body Java type
showBody	true	Output the in body

Example:

ID-claus-acer/3690-1214458315718/2-0 -> node3 To[mock:a] InOnly Properties:{CamelCauseException=null} Headers:{to=James} Body:Hello London

ID-claus-acer/3690-1214458315718/2-0 is the breadcrumb with the unique correlation id.
node3 is the id of the node in the route path. Is always shown.
To[mock:a] is the destination node.
InOnly is the exchange pattern. Is always shown.
Then the rest is properties, headers and the body.

Enabling

To enable tracer from the main run

java org.apache.camel.spring.Main -t

or

java org.apache.camel.spring.Main -trace

and the tracer will be active.

Enabling from Java DSL

The tracer can be enabled by adding it to the interceptor chain to the camel context. This is demonstrated in the unit test below.
Notice: We could have changed the properties on the Tracer object before adding it, if we e.g. don't like the default settings.

Error formatting macro: snippet: java.lang.NullPointerException

Running the test we get the trace information logged at INFO level:

2008-06-26 07:31:55,828 [main           ] INFO  TraceInterceptor               - ID-claus-acer/3690-1214458315718/2-0 -> node5 Interceptor[Delegate(Pipeline[DeadLetterChannel[Delegate(TraceInterceptor[Processor[MyProcessor]]), RecipientList[log:org.apache.camel.DeadLetterChannel?level=error], RedeliveryPolicy[maximumRedeliveries=6]], DeadLetterChannel[Delegate(TraceInterceptor[To[mock:a]]), RecipientList[log:org.apache.camel.DeadLetterChannel?level=error], RedeliveryPolicy[maximumRedeliveries=6]], DeadLetterChannel[Delegate(TraceInterceptor[To[mock:b]]), RecipientList[log:org.apache.camel.DeadLetterChannel?level=error], RedeliveryPolicy[maximumRedeliveries=6]]])] InOnly Properties:{} Headers:{to=James} Body:Hello London
2008-06-26 07:31:55,843 [main           ] INFO  TraceInterceptor               - ID-claus-acer/3690-1214458315718/2-0 -> node2 Processor[MyProcessor] InOnly Properties:{CamelCauseException=null} Headers:{to=James} Body:Hello London
2008-06-26 07:31:55,843 [main           ] INFO  TraceInterceptor               - ID-claus-acer/3690-1214458315718/2-0 -> node3 To[mock:a] InOnly Properties:{CamelCauseException=null} Headers:{to=James} Body:Hello London
2008-06-26 07:31:55,843 [main           ] INFO  TraceInterceptor               - ID-claus-acer/3690-1214458315718/2-0 -> node4 To[mock:b] InOnly Properties:{CamelCauseException=null} Headers:{to=James} Body:Hello London
2008-06-26 07:31:55,859 [main           ] INFO  TraceInterceptor               - ID-claus-acer/3690-1214458315718/2-1 -> node5 Interceptor[Delegate(Pipeline[DeadLetterChannel[Delegate(TraceInterceptor[Processor[MyProcessor]]), RecipientList[log:org.apache.camel.DeadLetterChannel?level=error], RedeliveryPolicy[maximumRedeliveries=6]], DeadLetterChannel[Delegate(TraceInterceptor[To[mock:a]]), RecipientList[log:org.apache.camel.DeadLetterChannel?level=error], RedeliveryPolicy[maximumRedeliveries=6]], DeadLetterChannel[Delegate(TraceInterceptor[To[mock:b]]), RecipientList[log:org.apache.camel.DeadLetterChannel?level=error], RedeliveryPolicy[maximumRedeliveries=6]]])] InOnly Properties:{} Headers:{from=Claus} Body:This is Copenhagen calling
2008-06-26 07:31:55,859 [main           ] INFO  TraceInterceptor               - ID-claus-acer/3690-1214458315718/2-1 -> node2 Processor[MyProcessor] InOnly Properties:{CamelCauseException=null} Headers:{from=Claus} Body:This is Copenhagen calling
2008-06-26 07:31:55,875 [main           ] INFO  TraceInterceptor               - ID-claus-acer/3690-1214458315718/2-1 -> node3 To[mock:a] InOnly Properties:{CamelCauseException=null} Headers:{from=Claus} Body:This is Copenhagen calling
2008-06-26 07:31:55,875 [main           ] INFO  TraceInterceptor               - ID-claus-acer/3690-1214458315718/2-1 -> node4 To[mock:b] InOnly Properties:{CamelCauseException=null} Headers:{from=Claus} Body:This is Copenhagen calling

Configuring from Java DSL

The tracer options can be configured from the Java DSL like this:

    public void configure() throws Exception {
        // add tracer as an interceptor so it will log the exchange executions at runtime
        // this can aid us to understand/see how the exchanges is routed etc.
        Tracer tracer = new Tracer();
        tracer.getFormatter().setShowBreadCrumb(false);
        tracer.getFormatter().setShowNode(false);
        ...
        getContext().addInterceptStrategy(tracer);

Enabling from Spring XML

There is now a trace attribute you can specify on the *<camelContext/> for example

  <camelContext trace="true" xmlns="http://activemq.apache.org/camel/schema/spring">
    ...
  </camelContext>

You can see this in action with the SpringTraceTest and its spring.xml file

Another option is to just include a spring XML which defines the Tracer bean such as the one that is automatically included if you run the Main with -t above.

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