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https://issues.apache.org/jira/browse/LOG4J2-3113?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17374733#comment-17374733
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Markus Spann commented on LOG4J2-3113:
--------------------------------------
Special treatment of {{StringBuilderFormattable}}. {{log4j2}} calls
{{formatTo}} not {{toString}} on objects of type {{StringBuilderFormattable}}:
{code:java}
java.util.function.Supplier<String> supplier = new
java.util.function.Supplier<>() {
@Override public String get() {return "Supplier.get";}
@Override public String toString() {return "Supplier.toString";}
};
org.apache.logging.log4j.util.StringBuilderFormattable sbf = new
org.apache.logging.log4j.util.StringBuilderFormattable() {
@Override public void formatTo(StringBuilder _sb)
{_sb.append("StringBuilderFormattable.formatTo");}
@Override public String toString() {return
"StringBuilderFormattable.toString";}
};
Logger logger = System.getLogger(StringBuildersSample.class.getName());
logger.log(Level.INFO, "Sample log: Supplier={}, StringBuilderFormattable={}",
supplier, sbf);
{code}
yields this log:
{noformat}
INFO [main] Sample log: Supplier=Supplier.toString,
StringBuilderFormattable=StringBuilderFormattable.formatTo{noformat}
> Support Supplier<> in varargs log message parameters
> ----------------------------------------------------
>
> Key: LOG4J2-3113
> URL: https://issues.apache.org/jira/browse/LOG4J2-3113
> Project: Log4j 2
> Issue Type: Improvement
> Components: API
> Affects Versions: 2.14.1
> Reporter: Markus Spann
> Priority: Minor
>
> It would be very useful, to give special treatment to message parameters of
> type {{java.util.function.Supplier<T>}} by calling {{get()}} rather than
> {{toString()}} on it while creating the log message.
> Message parameters (i.e. method calls that return the parameter) that are
> expensive to compute can thus be computed lazily.
> What's more, the logging call reads more naturally just like all other
> logging calls that use wildcards and parameters.
> {code:java}
> java.lang.System.Logger logger = System.getLogger("toto");
> // already supported style using a single Supplier
> logger.log(Level.DEBUG, () -> "Contents of array: " +
> Arrays.deepToString(array));{code}
> {code:java}
> // compiles but calls toString() rather than Supplier.get()
> logger.log(Level.DEBUG, "Contents of array: {}", (Supplier<String>) () ->
> Arrays.deepToString(array));{code}
> I've looked through the log4j2 Jira and found issue LOG4J2-599 in which a
> similar request was previously discussed without actually adding the feature
> to log4j2.
> (Note: Strangely Java requires the cast to (Supplier<String>).)
> My suggestion is to add Supplier support by enhancing method
> {{org.apache.logging.log4j.util.StringBuilders.appendSpecificTypes()}}.
> I will provide a Pull Request if you agree to the enhancement.
>
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