Commons Logging priority best practices

Question

This may be a purely subjective question (if no organization has attempted to standardize this), but my team struggles with this more than you would think.

We use Apache

Answer 1

I have always used this as a guideline; I use Log4j more than Commons Logging but this may still be helpful:

DEBUG - for genuinely debug-level info; will not be seen in production or shipped product, as INFO will be the minimum level; good for capturing timings, number of occurrences of events, etc

INFO - minimum level for production/shipped usage; record data likely to be useful in forensic investigations and to confirm successful outcomes ("stored 999 items in DB OK"); all info here must be such that you would be OK with end users/customers seeing it and sending you it, if need be (no secrets, no profanity!)

WARN - not an error level as such, but useful to know the system may be entering dodgy territory, e.g. business logic stuff like "number of ordered products < 0" which suggests a bug somewhere, but isn't a system exception; I tend not to use it that much to be honest, finding things tend to be more natural fits to INFO or ERROR

ERROR - use this for exceptions (unless there's a good reason to reduce to WARN or INFO); log full stacktraces along with important variable values without which diagnosis is impossible; use only for app/system errors, not bad business logic circumstances

FATAL - only use this for an error of such high severity that it literally prevents the app from starting / continuing

Additionally - review your logging often, both with DEBUG and INFO levels active, you want to be able to follow a good narrative through, with prominent events easy to find, and to make sure you're not doing anything too verbose which detracts from readability.

Also ensure you use a pattern which leads to neat columns for things like timestamps, source-classes and severity - again, it helps readability massively.