[slf4j-user] When more parameters than placeholders, extra parameters are not logged

[Erik van Oosten]

Hi Russ,

Mailing lists are not so popular anymore nowadays, chances that a sl4fj 
developer will respond here are not so good. Probably the best thing to 
do is write a feature request on https://github.com/qos-ch/slf4j/issues. 
A pull request is probably be appreciated as well!

Kind regards,
     Erik.


Op 25-01-2025 om 02:38 schreef Russ Block via slf4j-user:
> With this method or any similar method,
>     public void info(String format, Object... arguments) {
>         if (isInfoEnabled()) {
>             handleArgArrayCall(Level.INFO, null, format, arguments);
>         }
>     }
> If the number of objects in 'arguments' is more than the number of 
> placeholders, {}, the extra argument objects are not logged.  Is there 
> a reason for that?
>
> For example
>   public void setTemperature(Integer temperature) {
>     oldT = t;
>     t = temperature;
>   //Sent three parameters log with two placeholders
>   //Output "Temperature set to 90. Old value was null." The word extra 
> is not printed
>     logger.info("Temperature set to {}. Old value was {}.", t, oldT, 
> "extra");
>     if(temperature.intValue() > 50) {
>       logger.info("Temperature has risen above 50 degrees.");
>     }
>   }
>
>
> If I get into a situation where I have sent more argument objects than 
> placeholders that it should append those un-placed arguments to the 
> end of the logged string.  The intent of the developer is to have the 
> parameter logged. Finding this out from production is not good.  What 
> is sent to be logged is important information, depending on the log level.
>
> My use case is that I want to push some legacy code to start looking 
> like SLF4J so we can migrate away from the older pattern filled with 
> isLogTraceEnabled calls.  I learned of the above when I was writing 
> JUnit tests to see all the things the code would do and not do.
>
> I feel that https://www.slf4j.org/faq.html#logging_performance is 
> telling me that, in some way, the placeholder string substitution is 
> faster than appending multiple strings together.  I understood the 
> main point of the argument as converting items to string before I 
> needed them was where the overhead was.  Keeping them as type Object 
> reduces that overhead.
>
> I understand there are Sonarqube rules and PMD to prevent me from not 
> having the correct number of argument objects.  This would help, but I 
> feel like there are still going to be misses.  Since my code is 
> custom, Sonarqube and PMD do not feel like options.
>
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-- 
Erik van Oosten
e.vanoosten at grons.nl
https://day-to-day-stuff.blogspot.com
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