log4j regular expression? [{}]

Question

Hi I have a question regarding a log4j logger.

There is a part of the logger text I don't quite follow. The line looks as follows

logger.debug("Some text goes here [{}] and some more text here", someObject.function());

I had a look but I can't seem to find this as a regular expression, it smells strongly like it could be though and I suspect that it will be replaced by the returned value of someObject.function() much how one could replace string values in output by placing a %s. Would I be correct in this assumption? if not please elaborate as to what it does.

score 2 · Accepted Answer · edited May 23 '17 at 12:08

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It is not a regular expression. {} is a special syntax to print out objects and which is preferable over string concatenation. For example,

logger.debug("{}, {}", o1, o2); // 2 objects will be printed
logger.debug(o1 + ", " + o2); // the same in concatenation style

I suggest reading about advantages of formatting with {} instead of string concatenation.

I would like to add that most of the logging systems support asynchronous logging parameterized messages, it means you will always get an actual value (it doesn't guarantee by concatenation).

edited May 23 '17 at 12:08

Community

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answered Jul 05 '16 at 06:33

Andrew Tobilko

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Thanks for the extra info :) – Jul 05 '16 at 06:45

score 1 · Answer 2 · answered Jul 05 '16 at 06:32

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The value of someObject.function() will get replaced in {}

answered Jul 05 '16 at 06:32

rajesh

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log4j regular expression? [{}]

2 Answers2