Slf4j is definetly a great step forward. Log4j is restrictive for complex and
multi tenant apps like hadoop.
Also the fact that slf4j doesn't use any magic when binding to its log provider
makes it way easier to swap out its implementation then tools of the past.
> On Apr 10, 2014, at 2:16 AM, Steve Loughran <ste...@hortonworks.com> wrote:
>
> If we're thinking of future progress, here's a little low-level one: adopt
> SLF4J as the API for logging
>
>
> 1. its the new defacto standard of logging APIs
> 2. its a lot better than commons-logging with on demand Inline string
> expansion of varags arguments.
> 3. we already ship it, as jetty uses it
> 4. we already depend on it, client-side and server-side in the
> hadoop-auth package
> 5. it lets people log via logback if they want to. That's client-side,
> even if the server stays on log4j
> 6. It's way faster than using String.format()
>
>
> The best initial thing about SL4FJ is how it only expands its arguments
> string values if needed
>
> LOG.debug("Initialized, principal [{}] from keytab [{}]", principal,
> keytab);
>
> not logging at debug? No need to test first. That alone saves code and
> improves readability.
>
> The slf4 expansion code handles null values as well as calling toString()
> on non-null arguments. Oh and it does arrays too.
>
> int array = [1, 2, 3];
> String undef = null;
>
> LOG.info("a = {}, u = {}", array, undef) -> "a = [1, 2, 3], u = null"
>
> Switching to SLF4J from commons-logging is as trivial as changing the type
> of the logger created, but with one logger per class that does get
> expensive in terms of change. Moving to SLF4J across the board would be a
> big piece of work -but doable.
>
> Rather than push for a dramatic change why not adopt a policy of demanding
> it in new maven subprojects? hadoop-auth shows we permit it, so why not say
> "you MUST"?
>
> Once people have experience in using it, and are happy, then we could think
> about switching to the new APIs in the core modules. The only troublespot
> there is where code calls getLogger() on the commons log to get at the
> log4j appender -there's ~3 places in production code that does this, 200+
> in tests -tests that do it to turn back log levels. Those tests can stay
> with commons-logging, same for the production uses. Mixing commons-logging
> and slf4j isn't drastic -they both route to log4j or a.n.other back end.
>
> -Stevve
>
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