CODEWITHSUNDEEP
javalogging
assylias
assylias

Reputation: 328598

Logging good practice

I use sl4j / logback as a logging framework. I am unsure about the right way to log errors. Namely, assuming e is an Exception I want to log, I always hesitate between:

  1. logger.error("Something bad happened: {}\nError: {}", someInfo, e.getMessage());

    I understand this is not good practice because the stack trace is lost - not great to understand what happened.

  2. logger.error("Something bad happened: {}\nError: {}", someInfo, e.getMessage(), e);

    Using both e.getMessage() and e seems redundant, although I don't know if it is possible that e.getMessage() might contain extra information that would not be seen if I used:

  3. logger.error("Something bad happened: {}", someInfo, e);

    which is the syntax I generally use - but I want to make sure I am not missing anything.

Upvotes: 3

Views: 509

Answers (3)

Tony Hopkinson
Tony Hopkinson

Reputation: 20320

You definitely want the stack trace. Message is handy in circumstances where you've done something like "Error : Unable to find customer with ID : {0}", which may not be in the stacktrace. Trivial example but you get what I mean.

Another one for message is if you do the log as say a csv so you can analyse it. You can standarise message, and make filtering easier.

Last but not least redundant info in an error log, is way way way less of a problem, then the info you need not being in it. Err on the side of extreme verbosity is my guiding principle.

Oh this is for contrrolled access to a log file ,never say put stack trace as a response in asp for instance. Hackers wet dream that.

Upvotes: 1

Jens Schauder
Jens Schauder

Reputation: 81862

If you look at the source code of Throwable (http://www.docjar.com/html/api/java/lang/Throwable.java.html) you'll find that a Throwable when asked to print its stacktrace starts by priting itself, which prints its message.

I find it unlikely that anybody would change this behaviour, so your arguments are all correct and the 3. option is fine

Upvotes: 1

pcalcao
pcalcao

Reputation: 15975

I usually use number two, although I NEVER break one line of log into 2 lines (\n), although when printing the stack trace, it won't matter much (in all other cases, it creates too much visual entropy when your logs become really huge).

Why do I use number 2?

I want to see the message right away, on the first line, since it's the first thing that tells me what happened. Some might be expected and I can safely skip them, and some might not be.

In case I need to examine exactly what happened, I take a better look at the stack trace.

I reckon number 3 is also fine, since you'll get the information you need anyway. NEVER use option 1.

By the way, and just a particular opinion, saying that something bad happened on a ERROR line is a bit redundant ;)

Upvotes: 2

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