Logging

Using the Bukkit Logger

public class MyClass {

public void foo() {
    Logger logger = Bukkit.getLogger();
    
    logger.info("A log message");
    logger.log(Level.INFO, "Another message");
    logger.fine("A fine message");
    
        // logging an exception
        try {
            // code might throw an exception
        } catch (SomeException ex) {
            // log a warning printing "Something went wrong"
            // together with the exception message and stacktrace
            logger.log(Level.WARNING, "Something went wrong", ex);
        }

        String s = "Hello World!";

        // logging an object
        LOG.log(Level.FINER, "String s: {0}", s);

        // logging several objects
        LOG.log(Level.FINEST, "String s: {0} has length {1}", new Object[]{s, s.length()});
    }

}

Logging Levels

Java Logging Api has 7 levels. The levels in descending order are:

SEVERE (highest value)
WARNING
INFO
CONFIG
FINE
FINER
FINEST (lowest value)

The default level is INFO (but this depends on the system and used a virtual machine).

Note: There are also levels OFF (can be used to turn logging off) and ALL (the oposite of OFF).

Code example for this:

import java.util.logging.Logger;

public class Levels {
    private static final Logger logger = Bukkit.getLogger();

    public static void main(String[] args) {

        logger.severe("Message logged by SEVERE");
        logger.warning("Message logged by WARNING");
        logger.info("Message logged by INFO");
        logger.config("Message logged by CONFIG");
        logger.fine("Message logged by FINE");
        logger.finer("Message logged by FINER");
        logger.finest("Message logged by FINEST");

        // All of above methods are really just shortcut for
        // public void log(Level level, String msg):
        logger.log(Level.FINEST, "Message logged by FINEST");
    }
}

By default running this class will output only messages with level higher then CONFIG:

Jul 23, 2016 9:16:11 PM LevelsExample main
SEVERE: Message logged by SEVERE
Jul 23, 2016 9:16:11 PM LevelsExample main
WARNING: Message logged by WARNING
Jul 23, 2016 9:16:11 PM LevelsExample main
INFO: Message logged by INFO