log4j is an awesome logging library for Java. One thing I found out today is that you can change the logging level (debug, warn, info) at runtime, with a few lines of code.

// This monitors the log4j for changes over a specified period of milliseconds
PropertyConfigurator.configureAndWatch("./resources/log4j.properties", 60000);

What this function does is to tell log4j to check the configuration file every minute (60000 ms) for changes. So you can deploy a production server with only warn and error logging, but if something goes wrong you can enable debug and info logging (for example) simply by editing the configuration file and waiting a minute.

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