slf4j logging with jdk – how to enable debug?

Question

By default slf4j, when using with jdk (slf4j-jdk14-1.6.1.jar), does not log debug messages. How do I enable them?

I can’t find info neither in the official docs, the web or here on how to enable it.

I found some info on (failed though) creating a file in %JDK_HOME%/lib and defining the level there, in a config file. However, I would like to define the level at compile-/run-time so I can both run and debug my app from my IDE with different logging levels.

Isn’t there some environment variable I can set, or VM arg?

Answer 1

Why do you think it does not log DEBUG messages?

If you mean that your log.debug(String) logging calls do not end up in java.util.logging log files, then I guess you have to configure the logging.properties configuration file to allow log messages at FINE level.

If you do not want to mess with the global %JRE_HOME%/lib/logging.properties, then you can just pass in -Djava.util.logging.config.file=logging.properties on the command line - this will force the logging system to look for that configuration file in the current directory.

Or use some other (programmatic) way to configure java.util.logging, see below for tutorial.

This has nothing to do with configuring SLF4J; in fact, SLF4J does not have any configuration, everything is configured by simply swapping JAR files.

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For your reference:

• JDK14LoggerAdapter
• Java Logging API tutorial

Answer 2

If you are using slf4j SimpleLogger implementation read this.

There you can see that simpleLogger use INFO as default log level. You can change it by using a system property. This is usefull for non-production evironments:

static {      System.setProperty("org.slf4j.simpleLogger.defaultLogLevel", "trace"); }