Tuesday, April 04, 2017

Maven logging and the command line

I usually set up my Maven-build projects to be as quiet as possible. My preference is "Silence is Golden": if the command says nothing on the command line, it worked; if it failed, it prints to STDERR.

However, sometimes I want to see some output while I'm tracking down a problem. How best to reconcile these?

Maven 3.3.1 (maybe earlier) introduced the .mvn directory for your project root (note leading DOT). In here you can keep a jvm.config file which has the flags to the java command used when running mvn. Here's my usual jvm.config:


This quiets maven down quite a bit, using the properties to control Maven's more recent logger, SLF4J. And I normally commit that into my project code repository.

And for those times I'd like more output? I could edit the file, but I don't trust myself enough not to accidentally commit those temporary changes. So I use the command line:

$ MAVEN_OPTS='-Dorg.slf4j.simpleLogger.defaultLogLevel=INFO' mvn

Ultimately mvn reads .mvn/jvm.config, putting the contents into the variable MAVEN_OPTS, and uses MAVEN_OPTS in the invocation of java, and you can override the variable yourself on the command line.

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