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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.

Logging dependencies

Checkout which dependencies are required by Camel for logging purpose.

From Camel 2.12: the CamelContext must be explicitly configured for tracing:

  • XML:  <camelContext trace="true" ...>
  • Java: camelContext.setTracing(true).

Options

Option

Default

Description

destinationUri

null

Optional destination URI to route TraceEventExchange containing TraceEventMessage with details about the trace. Can be used for custom processing to store traces in database using JPA.

enabled

true

Enable/disable the tracer.

formatter

 

Sets the Trace Formatter to use.

Default: org.apache.camel.processor.interceptor.DefaultTraceFormatter.

jpaTraceEventMessageClassName

null

Camel 2.3: Fully qualified class name for a custom org.apache.camel.processor.interceptor.TraceEventMessage class which contains the traced information.

For example you can use your custom JPA @Entity class to store traced information in a database according to your schema layout.

logLevel

INFO

The logging level to use: FATAL, ERROR, WARN, INFO, DEBUG, TRACEOFF

logName

 

The log name to use.

Default: org.apache.camel.processor.interceptor.TraceInterceptor.

logStackTrace

false

Controls whether the stack trace of a traced exception should be logged. If false only the exception's class and message are logged.

traceFilter

null

An Exchange Predicate to filter the tracing.

traceInterceptors

false

Enable/disable tracing of interceptors.

traceExceptions

true

Enable/disable tracing of an exception thrown during the processing of an Exchange.

traceHandler

null

Camel 2.3: To use a custom org.apache.camel.processor.interceptor.TraceEventHandler where you can control what happens when a trace event occurs.

traceInterceptorFactory

null

Camel 2.3: To use a custom org.apache.camel.processor.interceptor.TraceInterceptorFactory where you can create the runtime trace instance which does the actual tracing. It should be a Processor instance.

Default: org.apache.camel.processor.interceptor.TraceInterceptor.

traceOutExchanges

false

Enable/disable fine grained tracing, using a callback, for both IN (before) and OUT (after).

By default only one trace callback is executed.

useJpa

false

To use a JpaTraceEventMessage from camel-jpa component as the TraceEventMessage. This requires that camel-jpa.jar is on the classpath.

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:

Option

Default

Description

breadCrumbLength

0

Fixed length of the bread crumb. 

0 = no fixed length.

Setting a value to e.g. 80 allows the tracer logs to be aligned for easier reading.

maxChars

 

Limits the number of chars logged per line.

From Camel 2.9: the default value is 10000.

multiline

false

Camel 2.18: If true each piece of information is logged on a new line.

nodeLength

0

Fixed length of the node. 

0 = no fixed length.

Setting a value to e.g. 40 allows the tracer logs to be aligned for easier reading.

showBody

true

Output the IN body.

showBodyType

true

Output the IN body Java type.

showBreadCrumb

true

Outputs the unique UnitOfWork for the exchange.

Can be used for correlation to identify a particular Exchange.

showException

true

Output the exception if the processing of an Exchange has failed.

showExchangeId

false

Enable/disable the output of an Exchange's unique id.

Currently the breadcrumb is sufficient.

showExchangePattern

true

Output the Message Exchange Pattern (MEP).

showHeaders

true

Output the IN message headers.

showNode

true

Previous and destination node.

Displayed as: from -> to.

showOutBody

false

Output the OUT (if any) body.

showOutBodyType

false

Output the OUT (if any) body Java type.

showOutHeaders

false

Output the OUT (if any) message headers.

showProperties

false

Output the Exchange's properties.

showRouteId

true

Camel 2.8: output the id of the route.

showShortExchangeId

false

To output the Exchange's unique id in short form, without the hostname.

Logging stream bodies

From Camel 2.8: the Camel Tracer will by default not log stream or files bodies. To force Camel to log these set the following property on the CamelContext properties:

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.

 

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:

Enable Tracing of OUT Messages

To trace the messages coming out of processing steps configure the tracer as follows:

Java DSL
 

or

Spring DSL
 

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:

 

And here we have our custom logger that implements the TraceFormatter interface where we can construct the log message how we like:

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).

Beware to access the original Exchange to avoid causing any side effects or alter its state. Prefer to access the information from TraceEventMessage

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:

 

 

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.

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:

And then our custom error processor where we can handle the exception and figure out at which node the exception occurred.

See Also

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