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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