Developer Fundamentals - Logging

Developer Fundamentals LOGGING BY AXEL IRRIGER (HTTP://WWW.AXELIRRIGER.DE) MAY, 2010

Agenda  About Myself  What Is Logging?  Storyboard  Analysis  Definition  Why Do We Want To Log Things?  How Do We Do Logging?  Logically  Technically

About Myself  Software/Solution Architect with a consulting company in Germany  Dealing with software since the age of 10  Atari ST … Basic, Assembler, Pascal  Primarily dealing with Java and Python nowadays  EAI, SOA, BPM  JBossAS 4 and JBossAS 5  Apache ServiceMix, jBPM, JBoss Rules  …  Passion  Software Quality  Excellence in Craftsmanship  Drop me a message axel (dot) irriger (at) gmail (dot) com

What Is Logging? - Storyboard John and Will are software developers. They are both experienced and get things done, literary speaken. On a tough assignment, they get errors and the software does not, what it should. Since they both short on schedule, they need to get that error fixed quickly, to not burn the deadline to ashes. What will they do?

What Is Logging? –John‘s Way John automatically fires up his favorite debugger and starts digging around the code, where it expects the error to be. After some hours passing, digging here, poking there, he located the error and got it fixed. It was in a different module than he first expected – but who cares, the job is done and the clock shows 11pm.

What Is Logging? –Will‘s Way Will gets curious – why in hell must this happen know? But it is, as it is. So, he fires up his IDE and reconfigures the logging system to „debug“ and starts the application again. After some 5-10 minutes looking through the log files, he gets curious – there‘s something wrong in this XYZ module. Though he doesn‘t know what. So, he again reconfigures the logging system again to „trace“ and starts his run again. Filtering out the logs pretty quickly he sees that gets wrong … that parameter should look different! He fixes the issue and starts again – everything‘s fine now. It‘s 6pm, a little late, but just in time for dinner.

What Is Logging? – Analysis  John did not care about logging – it just takes time and gets you nothing. That cost him time, overall  Will did care about logging, to be able to fix things faster  Logging helped him see, what the application did  He could locate the issue at hand more quickly and pin down the suspected piece of code  He needed not do any intense digging but just read output

What Is Logging? – Definition  Logging is about letting the program speak what it does  Using fine-grained thresholds, from the most generic to the most detailed information, information is written to a log  Logging is the process of noting down processing steps to document  What is done  With what data it is done  What the outcome is

Why Do We Want To Log Things?  Understanding and Documentation  Being able to provide good logging helps yourself to better understand the code  Reading through log messages helps new developers to more easily grasp your intentions  Bug fixing  Detect errors more easily  Detect strange variable values more easily  Find the error vs. Look for the error  Support  Really want to do endless iterations with a customer, or just get the logs and start working?

How Do We Do Logging? - Logically  What to log?  Method/Function entry and exist  You want to know where the program walks along  General information like starting, stopping, configuring  You want to see the „big picture“ of the program  External information and computations  You want explicitly see what can‘t be seen (RDBMS input, run-timecomputations, etc.)  Parameters passed  You want to see, how things happened and why  Log frameworks offer granularity – use it

How Do We Do Logging? - Logically  How should levels be used?  FATAL  everything which stops the program from continuing (no RDBMS, unable to read system files)  ERROR  everything which is erroneous, but does not stop te program from continuing (Mail adresses not found, so no mailing)  WARN  If defaults are used, because no configuration was passed and things like that  INFO  General informations  DEBUG  External informations, Control-Flow decisions  TRACE  Method/Function entry/exit, Parameters  Use this as a convention until you feel comfortable  When you‘re comfortable, adjust to your habbits

How Do We Do Logging? - Technically  Decide on the framework and stick to that  java.util.logging – Provided out of the box  Apache log4j (log4j) – The widest usage  Apache Commons::Logging (commons-logging) – Abstraction layer for other frameworks  Simple Logging Facade for Java (slf4j) – Simpler abstraction layer for other frameworks  Get familiar to your framework  How to use categories to filter things  How to filter out unimportant stuff  How to use appenders to utilize different log files  How to use loggers to support Console, File, SMTP, SNMP, ...  Always use something like „isDebugEnabled“ or „isLevelEnabled“  Don‘t even try to log something if it wouldn‘t be written  LOG.debug huge messages with „debug“ disabled has huge performance impact  Message will be serialized (costly) and then skipped!

Summary  We have seen why logging is worth a consideration  We have seen why we want to do logging at all  We have seen how logging should be approached logically („from the brain“)  We have seen how logging should be approached technically („from the keyboard“)  Various logging frameworks will be discussed in ongoing sessions Get out and your hands dirty!

Developer Fundamentals - Logging

by Axel Irriger on May 03, 2010

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