logging

Complete

Concept

Logging

recording certain information during a program’s execution
see how the system behaved before and during an issue
used for troubleshooting

Java logger class

java

import java.util.logging.Logger;
import java.util.logging.Level;

private static final Logger logger =
        Logger.getLogger(MyClass.class.getName()); // name of the class its logging for

logger.log(Level.INFO, "Application started");
logger.log(Level.WARNING, "Something suspicious happened");
logger.log(Level.SEVERE, "Critical failure");

Log levels

SEVERE (highest)
WARNING
INFO
CONFIG
FINE
FINER
FINEST

Filtering

logger only publishes messages that are >= to the set log level
ALL - show all levels
OFF - show nothing

java

logger.setLevel(Level.WARNING); // only WARNING and SEVERE are shown