Logger slf4j advantages of formatting with {} instead of string concatenation
Is there any advantage of using {} instead of string concatenation?
An example from slf4j
logger.debug("Temperature set to {}. Old temperature was {}.", t, oldT);
instead of
logger.debug("Temperature set to"+ t + ". Old temperature was " + oldT);
I think it's about speed optimization because parameters evaluation (and string concatenation) could be avoided in runtime depending on a config file. But only two parameters are possible, then sometimes there is no other choice than string concatenation. Needing views on this issue.
It is about string concatenation performance. It's potentially significant if your have dense logging statements.
(Prior to SLF4J 1.7) But only two parameters are possible
Because the vast majority of logging statements have 2 or fewer parameters, so SLF4J API up to version 1.6 covers (only) the majority of use cases. The API designers have provided overloaded methods with varargs parameters since API version 1.7.
For those cases where you need more than 2 and you're stuck with pre-1.7 SLF4J, then just use either string concatenation or new Object[] { param1, param2, param3, ... }. There should be few enough of them that the performance is not as important.
Short version: Yes it is faster, with less code!
String concatenation does a lot of work without knowing if it is needed or not (the traditional "is debugging enabled" test known from log4j), and should be avoided if possible, as the {} allows delaying the toString() call and string construction to after it has been decided if the event needs capturing or not. By having the logger format a single string the code becomes cleaner in my opinion.
You can provide any number of arguments. Note that if you use an old version of sljf4j and you have more than two arguments to {}, you must use the new Object[]{a,b,c,d} syntax to pass an array instead. See e.g. http://slf4j.org/apidocs/org/slf4j/Logger.html#debug(java.lang.String, java.lang.Object[]).
Regarding the speed: Ceki posted a benchmark a while back on one of the lists.