Question

With sl4fj if I want to construct a string message there is a nice approach which makes use of substitutions. For instance, it might be something like:

logger.info("Action {} occured on object {}.", objectA.getAction(), objectB);

If there are more than a few substitutions required then it is something like:

logger.info("Action {} occured on object {} with outcome {}.", 
    new Object[]{objectA.getAction(), objectB, outcome});

My question is: Is there a generic way for me to create a string (and not just a slf4j log message)? Something like:

String str = someMethod("Action {} occured on object {}.", objectA.getAction(), objectB);

or

String str = someMethod("Action {} occured on object {} with outcome {}.", 
    new Object[]{objectA.getAction(), objectB, outcome});

If it is in the standard Java library, what would that “someMethod” be?

Answer 1

String.format

String str = String.format("Action %s occured on object %s.",
   objectA.getAction(), objectB);

Or

String str = String.format("Action %s occured on object %s with outcome %s.",
   new Object[]{objectA.getAction(), objectB, outcome});

You can also use numeric positions, for example to switch the parameters around:

String str = String.format("Action %2$s occured on object %1$s.",
   objectA.getAction(), objectB);