[CONF] Apache Camel: Tracer (page edited)

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[CONF] Apache Camel: Tracer (page edited)

Dhiraj Bokde (Confluence)

Tracer has been edited by Claus Ibsen (Jan 19, 2009).

(View changes)

Content:

Tracer Interceptor

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.

You can enable or disable the Tracer's logging dynamically, by calling the tracer's setEnabled method.

The org.apache.camel.processor.interceptor.TraceFormatter has been rename to org.apache.camel.processor.interceptor.DefaultTraceFormatter in Camel 2.0.

Users of Camel 1.x should use TraceFormatter whereas 2.x users should use DefaultTraceFormatter.

Options

Trace has been improved in Camel 1.5 to be more configurable with these options:

Option Default Description
formatter   Sets the Trace Formatter to use. Will default use org.apache.camel.processor.interceptor.DefaultTraceFormatter.
enabled true Flag to enable or disable this tracer
logLevel INFO The logging level to use: FATAL, ERROR, WARN, INFO, DEBUG, TRACE
logName   The log name to use. Will default use org.apache.camel.processor.interceptor.TraceInterceptor.
traceFilter null An exchange Predicate to filter the tracing.
traceInterceptors false Flag to enable or disable tracing of interceptors
traceExceptions true Flag to enable or disable tracing of thrown exception during processing of the exchange
destinationUri null Camel 2.0: 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.

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
breadCrumbLength 0 Camel 1.5.1: 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.
nodeLength 0 Camel 1.5.1: 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.
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 In Camel 1.x its the destination node. In Camel 2.0 its both the previous and destination node, so you can see from -> to.
showExchangeId false To output the unique exchange id. Currently the breadcrumb is sufficient.
showShortExchangeId false Camel 1.5.1: To output the unique exchange id in short form, without the hostname.
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
showOutHeaders false Camel 2.0: Output the out (if any) message headers
showOutBodyType false Camel 2.0: Output the out (if any) body Java type
showOutBody false Camel 2.0: Output the out (if any) body
showExchangePattern true Camel 1.5: Output the exchange pattern
showException true Camel 1.5: Output the exception if the exchange has failed

Example:

ID-claus-acer/4412-1222625653890/2-0 -> to(mock:a)                , Pattern:InOnly , Headers:{to=James} , BodyType:String , 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.

Showing from and to

In Camel 2.0 the trace log will output both the from and to so you can see where the Exchange came from, such as:

>>> direct:start --> process(MyProcessor)
>>> process(MyProcessor) --> to(mock:a)
>>> to(mock:a) --> to(mock:b)

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.

public void testSendingSomeMessages() throws Exception {
    template.sendBodyAndHeader("direct:start", "Hello London", "to", "James");
    template.sendBodyAndHeader("direct:start", "This is Copenhagen calling", "from", "Claus");
}

protected RouteBuilder createRouteBuilder() throws Exception {
    return new RouteBuilder() {
        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.
            getContext().addInterceptStrategy(new Tracer());

            from("direct:start").
                    process(new Processor() {
                        public void process(Exchange exchange) throws Exception {
                            // do nothing
                        }

                        @Override
                        public String toString() {
                            return "MyProcessor";
                        }
                    }).
                    to("mock:a").
                    to("mock:b");
        }
    };
}

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

INFO  TraceInterceptor     - ID-claus-acer/4412-1222625653890/2-0 -> process(MyProcessor)      , Pattern:InOnly , Headers:{to=James} , BodyType:String , Body:Hello London 
INFO  TraceInterceptor     - ID-claus-acer/4412-1222625653890/2-0 -> to(mock:a)                , Pattern:InOnly , Headers:{to=James} , BodyType:String , Body:Hello London 
INFO  TraceInterceptor     - ID-claus-acer/4412-1222625653890/2-0 -> to(mock:b)                , Pattern:InOnly , Headers:{to=James} , BodyType:String , Body:Hello London 
INFO  TraceInterceptor     - ID-claus-acer/4412-1222625653890/2-1 -> process(MyProcessor)      , Pattern:InOnly , Headers:{from=Claus} , BodyType:String , Body:This is Copenhagen calling 
INFO  TraceInterceptor     - ID-claus-acer/4412-1222625653890/2-1 -> to(mock:a)                , Pattern:InOnly , Headers:{from=Claus} , BodyType:String , Body:This is Copenhagen calling 
INFO  TraceInterceptor     - ID-claus-acer/4412-1222625653890/2-1 -> to(mock:b)                , Pattern:InOnly , Headers:{from=Claus} , BodyType:String , 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);

Using predicates to filter exchanges

Available as of Camel 1.5
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:

Tracer tracer = new Tracer();
    // set the level to FATAL so we can easily spot it
    tracer.setLogLevel(LoggingLevel.FATAL);
    // and only trace if the body contains London as text
    tracer.setTraceFilter(body().contains(constant("London")));
    // do not show exchange pattern
    tracer.getFormatter().setShowExchangePattern(false);

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.

Configuration from Spring

In Camel 1.5 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.

<!-- we can configure the tracer by defining the tracer bean and set the properties as we like -->
<!-- the id name can be anything its the class that must be org.apache.camel.processor.interceptor.Tracer -->
<bean id="camelTracer" class="org.apache.camel.processor.interceptor.Tracer">
    <property name="traceExceptions" value="false"/>
    <property name="traceInterceptors" value="true"/>
    <property name="logLevel" value="FATAL"/>
    <property name="logName" value="com.mycompany.messages"/>
</bean>

<camelContext id="camel" trace="true" xmlns="http://activemq.apache.org/camel/schema/spring">
    <route>
        <from uri="direct:start"/>
        <to uri="mock:result"/>
    </route>
</camelContext>

Formatting from Spring

In Camel 1.5 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 formatter, as the example below illustrates:

<bean id="traceFormatter" class="org.apache.camel.processor.interceptor.DefaultTraceFormatter">
    <property name="showBody" value="true"/>
    <property name="showBodyType" value="false"/>
    <property name="showBreadCrumb" value="false"/>
</bean>

<camelContext id="camel" trace="true" xmlns="http://activemq.apache.org/camel/schema/spring">
    <route>
        <from uri="direct:start"/>
        <to uri="mock:result"/>
    </route>
</camelContext>

Enable tracing of out messages

Available as of Camel 2.0

You can now trace messages coming out of processing steps. To enable this, configure the tracer as follows

Tracer tracer = new Tracer();
tracer.setTraceOutExchanges(true);

// we configure the default trace formatter where we can
// specify which fields we want in the output
DefaultTraceFormatter formatter = new DefaultTraceFormatter();
formatter.setShowOutBody(true);
formatter.setShowOutBodyType(true);

// set to use our formatter
tracer.setFormatter(formatter);

getContext().addInterceptStrategy(tracer);

or

<bean id="camelTracer" class="org.apache.camel.processor.interceptor.Tracer">
  <property name="traceOutExchanges" value="true" />
</bean>

<bean id="traceFormatter" class="org.apache.camel.processor.interceptor.DefaultTraceFormatter">
  <property name="showOutBody" value="true" />
  <property name="showOutBodyType" value="true" />
</bean>

Running with these options, you'll get output similar to:

INFO  TraceInterceptor - ID-mojo/59899-1225474989226/2-0 -> transform(body) , Pattern:InOnly , Headers:{to=James} , BodyType:String , Body:Hello London
INFO  TraceInterceptor - transform(body) -> ID-mojo/59899-1225474989226/2-0 , Pattern:InOnly , Headers:{to=James} , BodyType:String , Body:Hello London , OutBodyType:String , OutBody:Hello London

Using Custom Formatter

Avaiable as of Camel 2.0

You can now implement your own org.apache.camel.processor.interceptor.TraceFormatter to be used for logging trace messages to the log.

The sample below shows how to configure a Tracer from Java DSL using custom formatter:

// we create a tracer where we want to use our own formatter instead of the default one
Tracer tracer = new Tracer();

// use our own formatter instead of the default one
MyTraceFormatter formatter = new MyTraceFormatter();
tracer.setFormatter(formatter);

// and we must remeber to add the tracer to Camel
getContext().addInterceptStrategy(tracer);

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

// here we have out own formatter where we can create the output we want for trace logs
// as this is a test we just create a simple string with * around the body
class MyTraceFormatter implements TraceFormatter {

    public Object format(TraceInterceptor interceptor, ProcessorType node, Exchange exchange) {
        return "***" + exchange.getIn().getBody(String.class) + "***";
    }
}

Using Destination for custom processing and routing

Avaiable as of Camel 2.0

Tracer now 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 TraceEventExchange 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 be accessed using getTracedExchange()

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 TraceEventExchange 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:

// we create a tracer where we want to send TraveEvents to an endpoint
// "direct:traced" where we can do some custom processing such as storing
// it in a file or a database
Tracer tracer = new Tracer();
tracer.setDestinationUri("direct:traced");
// we disable regular trace logging in the log file. You can omit this and
// have both.
tracer.setLogLevel(LoggingLevel.OFF);
// and we must remeber to add the tracer to Camel
getContext().addInterceptStrategy(tracer);

Then we can configure a route for the traced messages:

from("direct:traced").process(new MyTraceMessageProcessor()).to("file://myapp/logs/trace);

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.

class MyTraceMessageProcessor implements Processor {

    public void process(Exchange exchange) throws Exception {
        // here we can transform the message how we like want it
        TraceEventMessage msg = exchange.getIn().getBody(DefaultTraceEventMessage.class);

        // we want to store it as a CSV with from;to;exchangeId;body
        String s = msg.getFromEndpointUri() + ";" + msg.getToNode() + ";" + msg.getExchangeId() + ";" + msg.getBody();

        // so we replace the IN body with our CSV string
        exchange.getIn().setBody(s);
    }
}

Using JPA as datastore for trace messages

Avaiable as of Camel 2.0

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

See Also