Logger slf4j advantages of formatting with instead of string concatenation

Question

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

User · Answer

Since  String is immutable in Java  so the left and right String have to be copied into the new String for every pair of concatenation  So  better go for the placeholder

User · Answer

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

User · Answer

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

User · Answer

I think from the author s point of view  the main reason is to reduce the overhead for string concatenation I just read the logger s documentation  you could find following words          lt p gt This form avoids superfluous string concatenation when the logger   is disabled for the DEBUG level  However  this variant incurs the hidden    and relatively small  cost of creating an  lt code gt Object   lt  code gt  before    invoking the method    even if this logger is disabled for DEBUG  The variants taking     link  debug String  Object  one  and   link  debug String  Object  Object  two    arguments exist solely in order to avoid this hidden cost  lt  p gt           param format    the format string     param arguments a list of 3 or more arguments     public void debug String format  Object    arguments

User · Answer

Another alternative is String format    We are using it in jcabi-log  static utility wrapper around slf4j    Logger debug this   some variable    s   value     It s much more maintainable and extendable  Besides  it s easy to translate

[optimization] Logger slf4j advantages of formatting with {} instead of string concatenation

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