Paul Smith wrote:
If logger implements org.slf4j.Logger, then one can write
String name = "Scott";
logger.debug("Hello Scott");
logger.debug("Hello {}", name);
Both log statements will print as "Hello Scott". However, the latter
log statement will contain 'name' as a parameter. The SLF4J
implementation can choose to preserve or to discard this parameter in
the LoggingEvent.
SLF4J allows for 0,1,2 or an array of parameters. Thus, you can write
Map aMap = ...;
List aList = ...;
logger.debug("Hello", new Object[]{new Integer(37), aMap, aList});
First off, I've come back from some leave, and prior to that was
extremely overloaded at work, so my attention to detail on this thread
is limited.
Am I correct in distilling that the crux of the _driver_ to do this is
to support the above, and only that feature? This is 'nice' but really
not that high a priority I would have thought.. Given the vast majority
of people are on Java5+ platforms, a source and binary compatible way is
to introduce a simple 'log4j-java5plus' extension jar that has something
like this:
Support for parameterized logging is helpful. However, the main impetus is to
converge on a logging API for benefit of the java community. The benefit for
log4j may not be obvious at first, but the fact that it natively implements
SLF4J will enhance log4j's stature as well. This may be doubtful coming from me,
the author of SLF4J, but also log4j. Nevertheless, if you stop and think for a
second, it makes sense. My proposal is not only about log4j but about logging in
java. As log4j committer, here is your chance to shape the future of java
logging in a constructive way.
Of course, there is the temptation to believe that log4j is such a grand name
that it does need to adapt to changing circumstances. Don't succumb to that.
public class LogUtils {
..
public static void debug(Logger log, String message, Object... args) {
if (!log.isDebugEnabled()) {
return;
}
log.debug(getFormattedMessage(message, args));
}
..
private static String getFormattedMessage(String message, Object...
args) {
String formattedMessage = message;
if (args != null && args.length > 0) {
formattedMessage = String.format(message, args);
}
return formattedMessage;
}
..
Then the code is changed to:
LogUtils.debug(LOG, "Hello %s, your age is %d", name, age);
SLF4J's message formatting mechanism is extremely simple and very fast. It is
also very convenient, considering the most common cases. Your suggestion, offers
more flexibility and power, but which is not needed under most circumstances.
Now, that bypasses slf4j completely, and maintains source &
binary compatibly, and can easily be migrated to. My point is not to
suggest log4j introduce the above, or to dissuade from considering slf4j
integration more generally, but if the above feature is it... it really
doesn't seem like a massive driver that breaks binary compatibility and
possibly alienate a whole bunch of people (which it could, and that
could badly tarnish the log4j 'brand' as it were).
Quoting LOG4J2-27:
There is actually a way to maintain 100% source code compatibility. The
org.apache.log4j.Logger/Category classes would retain their existing method
signatures but would delegate to org.apache.log4j.impl.Logger class which would
implement the org.slf4j.Logger interface. This is feasible as demonstrated by
the log4j-over-slf4j module in SLF4J. See
http://slf4j.org/legacy.html#log4j-over-slf4j
Clients wishing to use the existing log4j classes could continue to do so. Those
wishing to standardize on the SLF4J API could do so as well. Direct use of
org.apache.log4j.impl.Logger would technically be possible but discouraged.
So I'm not in favour of rushing any decision at all.
The SLF4J debate has been ongoing for several years. Now that it has established
itself as a credible API, it is time to reconsider the question under new light.
Paul
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