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javalogginglog4jlogbacktostring

Improving detail printing in log4j

I have the following code. The log level is INFO. How can we write the better code that the toString will not be executed ?

Set<Integer> resultUserIdsSet = new HashSet<>();
log.trace("userIdsSet={}", resultUserIdsSet.toString());

Note: The resultUserIdsSet contains milions of integers.

We use ch.qos.logback:logback-classic:jar:1.2.3

Solution

  • Everyone is telling you to use a Supplier, but there is no need for that. Just let the logger do the toString call:

    log.trace("userIdsSet={}", resultUserIdsSet);

    By removing .toString(), you are just passing a reference to the Set. If the trace level is not enabled, the logger call returns immediately; the cost is essentially negligible.

    If and only if the trace level is enabled, then the logger will invoke toString() on the Set.