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https://issues.apache.org/jira/browse/LOG4J2-599?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14658248#comment-14658248
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Remko Popma commented on LOG4J2-599:
------------------------------------
I like Jason's idea. I experimented a little and it seems to work.
Nick's idea to use the existing {{log(String, Object...)}} methods does not
seem to work. The following simple client program did not compile:
{code}
// Does not compile with our current Logger API: Eclipse complains that
// "The method trace(String, Object...) in the type Logger is not applicable
for the arguments (String, () -> {})"
logger.trace("Expensive parameter {}", () -> new SecureRandom().nextLong());
{code}
An alternative is to add corresponding {{log(String, Callable<?>...)}}
methods. This solves the compilation problem. It also means that clients cannot
mix lambda parameters with object parameters: clients need to provide either
all objects or all lambda expressions as parameters. (Sounds reasonable to me.)
I propose adding the following methods to the {{Logger}} API:
* trace(Marker, Callable<?>)
* trace(Marker, Callable<?>, Throwable)
* trace(Marker, String, Callable<?>...)
* trace(Callable<?>)
* trace(Callable<?>, Throwable)
* trace(String, Callable<?>...)
* ... same for all other log levels
Client code using Java 6 or 7 would work unchanged (unlikely they will use
these new methods):
{code}
// client code using Java 6 or 7 would continue to use this style
if (logger.isDebugEnabled()) {
logger.debug("I am expensive to compute {}", someExpensiveMethodCall();
}
{code}
and users on Java 8 now have the option to replace the above with a single
lambda expression:
{code}
// client code using Java 8 can use a lambda expression,
// no longer needing to check if the DEBUG level is enabled
logger.debug("I am expensive to compute {}", () -> someExpensiveMethodCall();
{code}
Thoughts?
> Support lambda functions (or similar) for log message parameters
> ----------------------------------------------------------------
>
> Key: LOG4J2-599
> URL: https://issues.apache.org/jira/browse/LOG4J2-599
> Project: Log4j 2
> Issue Type: Brainstorming
> Components: Core
> Reporter: Matt Sicker
> Priority: Minor
> Labels: Java8
>
> It would be nice if we could support 0-param lambda functions (or the
> equivalent: interfaces with a single empty-parameter message call), or more
> simply, allow Runnables (or something similar) to be passed which will be
> dynamically executed if the log message is enabled.
> The use case here is that although string construction of the log message is
> a performance issue that is already solved quite well, the problem of adding
> in information to the log message that makes other calculations still needs
> to be wrapped in an if check.
> I'm not sure if it'd be best to just use Runnable, or create a new interface,
> or try to emulate how Java 1.8 lambdas work via an interface with a single
> method defined. The details here would still need to be fleshed out, but I
> think this sort of feature could be rather handy (especially in a Java 1.8+
> environment, or in Groovy/Scala/etc.).
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