In this example, we will learn how to change Java Util Logging default level to a new value.

To change a log level we must use Logger#setLevel() and Handler#setLevel().

Examples

Programmatically setting Log Level

We are going to set the log Level to ALL on the root logger/handlers, then we will find out all declared Levels in the Level class via reflection and then we will use the log() method on them. We will also set a custom easy to read log format.

public class LogLevelExample {
    private static Logger log = Logger.getLogger(LogLevelExample.class.getName());

    static {
        System.setProperty("java.util.logging.SimpleFormatter.format",
                "[%1$tF %1$tT %1$tL] [%4$-7s] %5$s %n");
    }

    public static void main(String[] args) throws Exception {
        setLevel(Level.ALL);
        Set<Level> levels = getAllLevels();
        int i = 1;
        for (Level level : levels) {
            log.log(level, level.getName() + " - " + (i++));
        }
    }

    public static void setLevel(Level targetLevel) {
        Logger root = Logger.getLogger("");
        root.setLevel(targetLevel);
        for (Handler handler : root.getHandlers()) {
            handler.setLevel(targetLevel);
        }
        System.out.println("level set: " + targetLevel.getName());
    }

    public static Set<Level> getAllLevels() throws IllegalAccessException {
        Class<Level> levelClass = Level.class;

        Set<Level> allLevels = new TreeSet<>(
                Comparator.comparingInt(Level::intValue));

        for (Field field : levelClass.getDeclaredFields()) {
            if (field.getType() == Level.class) {
                allLevels.add((Level) field.get(null));
            }
        }
        return allLevels;
    }
}

Output

level set: ALL
[2025-10-29 09:37:50 511] [ALL    ] ALL - 1 
[2025-10-29 09:37:50 513] [FINEST ] FINEST - 2 
[2025-10-29 09:37:50 514] [FINER  ] FINER - 3 
[2025-10-29 09:37:50 514] [FINE   ] FINE - 4 
[2025-10-29 09:37:50 514] [CONFIG ] CONFIG - 5 
[2025-10-29 09:37:50 514] [INFO   ] INFO - 6 
[2025-10-29 09:37:50 516] [WARNING] WARNING - 7 
[2025-10-29 09:37:50 516] [SEVERE ] SEVERE - 8 
[2025-10-29 09:37:50 516] [OFF    ] OFF - 9 

Setting Level in properties file

We are going to set FINEST level:

src/main/resources/logging.properties

handlers= java.util.logging.ConsoleHandler
.level= FINEST
java.util.logging.ConsoleHandler.level = FINEST
java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter
java.util.logging.SimpleFormatter.format=[%1$tF %1$tT] [%4$-7s] %5$s %n

public class LogLevelPropertiesExample {
    private static Logger log;

    static {
        String path = LogLevelPropertiesExample.class
                .getClassLoader()
                .getResource("logging.properties")
                .getFile();
        System.setProperty("java.util.logging.config.file", path);
        log = Logger.getLogger(LogLevelPropertiesExample.class.getName());
    }

    public static void main(String[] args) throws Exception {
        Set<Level> levels = getAllLevels();
        int i = 1;
        for (Level level : levels) {
            log.log(level, level.getName() + " - " + (i++));
        }
    }
    .............
}

[2017-09-20 23:49:20] [FINEST ] FINEST - 2 
[2017-09-20 23:49:20] [FINER  ] FINER - 3 
[2017-09-20 23:49:20] [FINE   ] FINE - 4 
[2017-09-20 23:49:20] [CONFIG ] CONFIG - 5 
[2017-09-20 23:49:20] [INFO   ] INFO - 6 
[2017-09-20 23:49:20] [WARNING] WARNING - 7 
[2017-09-20 23:49:20] [SEVERE ] SEVERE - 8 
[2017-09-20 23:49:20] [OFF    ] OFF - 9 

The default log Level

The default level is INFO. If we don't set the level in either of above examples then output would be:

[2017-09-20 23:51:45 801] [INFO   ] INFO - 6
[2017-09-20 23:51:45 834] [WARNING] WARNING - 7
[2017-09-20 23:51:45 834] [SEVERE ] SEVERE - 8
[2017-09-20 23:51:45 834] [OFF    ] OFF - 9

Example Project

Dependencies and Technologies Used:

• JDK 1.8
• Maven 3.3.9