Tracer Interceptor

Camel's tracer interceptor can be used for logging, by default at the INFO level, a route's execution. The tracer is an instance of org.apache.camel.spi.InterceptStrategy. It can be applied to either a DefaultCamelContext or a SpringCamelContext to ensure that there is a TracerInterceptor created for every node in the route. The tracer's logging can be enabled/disabled dynamically by calling its setEnabled method.

Options

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. By default the tracer uses: org.apache.camel.processor.interceptor.DefaultTraceFormatter to format the log line.

DefaultTraceFormatter has the following options:

Example:

where:

• 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. Always displayed.
• To[mock:a] is the destination node.
• InOnly is the exchange pattern. Is always shown.
• Then the rest is properties, headers and the body.

Showing from and to

The trace log will output both the from and to so you can see where the Exchange came from, such as:

Enabling

To enable tracer from the main run:

or

and the tracer will be activated.

Enabling in Java

You can configure tracing at a higher granularity as you can configure it on camel context and then override and set it per route as well. For instance you could just enable the tracer for a particular route.

Configuring in Java

Tracer options can be configured in Java as follows:

Using Predicates to Filter Exchanges

In the code below we want the tracer only to trace if the body contains the text London. As this is just an example can of course set any Predicate that matches your criteria:

Enabling in Spring XML

There is now a trace attribute you can specify on the <camelContext/>.

Example:

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.

Configuring in Spring XML

You can configure the tracer as a Spring bean. Just add a bean with the bean class org.apache.camel.processor.interceptor.Tracer and Camel will use it as the tracer.{snippet:id=e1|lang=xml|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/interceptor/tracerConfigurationTest.xml} 

You can configure the formatting of tracer as a Spring bean. Just add a bean with the id="traceFormatter" and Camel will lookup this id and use the associated formatter.

Example:{snippet:id=e1|lang=xml|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/interceptor/traceFormatterTest.xml}

Enable Tracing of OUT Messages

To trace the messages coming out of processing steps configure the tracer as follows:{snippet:id=tracingOutExchanges|title=Java DSL|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/TraceInterceptorWithOutBodyTraceTest.java} 

or{snippet:id=tracingOutExchanges|title=Spring DSL|lang=xml|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/traceInterceptorWithOutBodyTrace.xml} 

With these options the output will look like:

Using a Custom Formatter

To create a custom formatter create a class that implements the interface org.apache.camel.processor.interceptor.TraceFormatter.

Example:{snippet:id=e1|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/interceptor/TraceFormatterTest.java} 

And here we have our custom logger that implements the TraceFormatter interface where we can construct the log message how we like:{snippet:id=e2|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/interceptor/TraceFormatterTest.java}

Using a Destination for Custom Processing and Routing

Tracer supports custom processing of trace events. This can be used to route a trace event to a JPA endpoint for persistence in a database.

This works by Camel creates a new TraceEventMessage containing:

• snapshot of the original traced Exchange as a immutable TraceEventMessage containing String values of the fields, when the interception occurred. This ensures the fields contains the exact data at the given time of interception.
• the original Exchange can in some implementations be accessed using getTracedExchange() (though with JPA based tracer you cannot get the original Exchange).

Camel routes the TraceEventMessage synchronously from the point of interception. When its completed Camel will continue routing the original Exchange.

The sample below demonstrates this feature, where we route traced Exchanges to the direct:traced route:{snippet:id=e1|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/interceptor/TraceInterceptorDestinationTest.java} 

Then we can configure a route for the traced messages:

And our processor where we can process the TraceEventMessage. Here we want to create a CSV format of the trace event to be stored as a file. We do this by constructing the CSV String and the replace the IN body with our String instead of the TraceEventMessage.{snippet:id=e2|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/interceptor/TraceInterceptorDestinationTest.java}

Using JPA as a Datastore for Trace Messages

See Tracer Example for complete documentation and how to use this feature.

Traced Route Path During Runtime

Tracer also traces the actual route path taken during runtime. Camel will store the route path taken on the UnitOfWork when Tracer is enabled. The example below demonstrates how we can use that for error handling where we can determine at which node in the route graph the error triggered.

First we define our route:{snippet:id=e1|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/TraceableUnitOfWorkTest.java}And then our custom error processor where we can handle the exception and figure out at which node the exception occurred.{snippet:id=e2|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/TraceableUnitOfWorkTest.java}

See Also

• Tracer Example
• Debugger
• Delay Interceptor
• Log