Tuesday, September 3, 2013

Exploring Apache Camel Core - Log Component

There are many ways to log and inspect the messages as it pass through your Camel Route. The camel-core comes with a log component that let you inspect the message. So instead of write a separate Processor just to log a line as got processed, try using this:

from("timer://timer1?period=1s")
.to("log:demo")

By default, the log component will record your message body content through your logger name, demo in above case, at INFO level. Since you can give any name, you can control the logging LEVEL anyway you like through a Camel SLF4J logger implementation.

To log the message in DEBUG level, try this

from("timer://timer1?period=1s")
.to("log:demo?level=DEBUG")

Now if you use log4j as logger implementation, then ensure to add a logger config like this.

log4j.logger.demo = DEBUG
log4j.logger.org.apache.camel = INFO

The Camel message may have Properties and Headers as well, so to display these, you may add showAll=true.

When you process messages that have large body text, it might be more practical to just dislay certain number of characters. To do this, add maxChars=256 to URL.

How to measure Camel messages throughput rate

One of the hidden gem of the log componet is its ability to log messages throughput! You may specific group of messages to be logged, and once it reached that count, it will print the msgs/sec rate output. To enable this, just add groupSize option to URL.

To demo this, I will create a SampleGenerator bean processor that would flood the Route with sample messages. I will use the Camel context registry to bind the bean, and then reference it in the Route. Here is the demo code.

package camelcoredemo;

import org.slf4j.*;
import org.apache.camel.*;
import org.apache.camel.builder.*;
import org.apache.camel.main.Main;

public class LogDemoCamel extends Main {
    static Logger LOG = LoggerFactory.getLogger(LogDemoCamel.class);
    public static void main(String[] args) throws Exception {
        LogDemoCamel main = new LogDemoCamel();
        main.enableHangupSupport();
        main.addRouteBuilder(createRouteBuilder());
        main.bind("sampleGenerator", new SampleGenerator());
        main.run(args);
    }
    static RouteBuilder createRouteBuilder() {
        return new RouteBuilder() {
            public void configure() {
                from("bean:sampleGenerator")
                .to("log://demo?groupSize=100");
            }
        };
    }
    static class SampleGenerator implements Processor{
        int count = 0;
        public void process(Exchange msg) throws Exception {
            if (count >= 500){
                LOG.info("Max count has reached. Do nothing.");
                Thread.sleep(Long.MAX_VALUE);
                return;
            }

            // Let's generate sample message.
            count++;
            LOG.trace("Generating sample msg #{}", count);
            msg.getOut().setBody("Sample msg");
        }
    }
}

Now you should able to compile and run this demo.

mvn compile exec:java -Dexec.mainClass=camelcoredemo.LogDemoCamel

When running this demo, you will notice the rate will be displayed on console and how fast you can pump message to Route and to process it. This is a very useful feature to help you measure and have a quick view on your Route's capability.

There are more options availabe from Log component that you may explore. Try it out with a Route and see it for yourself.