Logback pattern - do replace if message doesn't contain a word - regex

Question

This is a follow-up question for How to prevent logback/slf4j from parsing a new line character
I use following pattern to avoid strings with \n breaking into new line. But after using this pattern, my stacktraces come up with \n in the beginning which looks awkward.
<pattern>[%d{dd MMM yyyy HH:mm:ss,SSS}] [%5p] [%X{sid}] [%-20C{0} %25M]:[%-4L] - %replace(%m){'\n', '\\n'}%n</pattern>
Result stacktrace:
[21 Feb 2015 23:14:24] [ERROR] [21181422764] [myclass mymethod]:[221] - Socket exception occured while sending request for user. Stacktrace:= java.net.ConnectException: Connection refused: connect
\n at java.net.DualStackPlainSocketImpl.connect0(Native Method)
I've to change the replace to match only those %m that do not have "Exception" word in them. Not sure how to accomplish this in pattern. Also, I'm concerned about how this overall match and replace is adding to logging time cost and if it is acceptable cost.

Answer 1

It looks like you're manually formatting the exception as part of your message, but logback does this for you if you include the exception as an argument of the log call (see SLF4J API). I recommend using that API instead of attempting to include it in your message.
final Logger log = LoggerFactory.getLogger(Foo.class);
try {
// ...
} catch (IOException e) {
log.error("Socket exception occurred while sending request for user.", e);
}
If you're concerned with performance, note that by default, logback includes packaging information for each method in the stacktrace, which could be expensive, especially if your application frequently logs exceptions. To skip the package-info lookup, append %ex to your pattern layout.
In your example:
<pattern>... %replace(%m){'\n', '\\n'}%n%ex</pattern>