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From "Remko Popma (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LOG4J2-599) Support lambda functions (or similar) for log message parameters
Date Thu, 06 Aug 2015 23:04:06 GMT

    [ https://issues.apache.org/jira/browse/LOG4J2-599?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14660945#comment-14660945

Remko Popma commented on LOG4J2-599:

That is the use case for this ticket: users on Java 8 will be able to avoid the explicit level
check and instead write 
logger.trace("Some expensive operation returned {}", () -> expensiveOperation());

resulting in more compact and cleaner code.

The only logging product that I am aware of that currently supports lambda expressions for
lazy logging is the JDK [Logger|http://docs.oracle.com/javase/8/docs/api/java/util/logging/Logger.html#log-java.util.logging.Level-java.util.function.Supplier-].
But IMHO the JDK Logger is only doing a partial job: it only lazily constructs the whole log
message. There is no API for lazily constructing message parameters.

I think keeping up to date with Java language developments makes this a "strategic" feature
that adds to the reasons why Log4j 2 is the logging library of choice for our users.

> 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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