How do I set the formatter of logger handlers?

By Wayan in Logging 0 Comment

In this example we’ll see how to set the formatter for the logger handlers. We set the formatter by calling the Handler.setFormatter() method. In the code below we set a SimpleFormatter for our FileHandler handler and XMLFormatter for the ConsoleHandler handler.

This SimpleFormatter format the log in a plain text information while on the other side the XMLFormatter format the log record in XML format.

package org.kodejava.util.logging;

import java.util.logging.*;
import java.io.IOException;

public class LogFormatter {
    public static void main(String[] args) {
        Logger logger = Logger.getLogger(LogFormatter.class.getName());

        try {
            // Create a FileHandler that will log to mylog.txt with a
            // SimpleFormatter.
            FileHandler simpleHandler = new FileHandler("mylog.txt", true);
            simpleHandler.setFormatter(new SimpleFormatter());
            logger.addHandler(simpleHandler);

            // Create a ConsoleHandler that will log to the console with
            // an XMLFormatter.
            ConsoleHandler consoleHandler = new ConsoleHandler();
            consoleHandler.setFormatter(new XMLFormatter());
            logger.addHandler(consoleHandler);

            // Do not send the message to parent handlers.
            logger.setUseParentHandlers(false);
        } catch (IOException e) {
            logger.log(Level.SEVERE, "Fail to create logger file handler.", e);
        }

        logger.info("Logging application information message.");
        logger.warning("Logging application warning message.");
    }
}

How do I compare Logger Level severity?

By Wayan in Logging 0 Comment

In this example we see how we can compare the Level severity between two levels. The Level class has an intValue() method that return the integer value of Level‘s severity.

package org.kodejava.util.logging;

import java.util.logging.Level;

public class LogLevelSeverityCompare {
    public static void main(String[] args) {
        Level info = Level.INFO;
        Level warning = Level.WARNING;
        Level finest = Level.FINEST;

        // To compare the Level severity we compare the intValue of the Level.
        // Each level is assigned a unique integer value as the severity
        // weight of the level.
        if (info.intValue() < warning.intValue()) {
            System.out.printf("%s (%d) is less severe than %s (%d)%n",
                    info, info.intValue(), warning, warning.intValue());
        }

        if (finest.intValue() < info.intValue()) {
            System.out.printf("%s (%d) is less severe than %s (%d)%n",
                    finest, finest.intValue(), info, info.intValue());
        }
    }
}

When we run the program above will see the following result:

INFO (800) is less severe than WARNING (900)
FINEST (300) is less severe than INFO (800)

How do I get the current Level of a Logger?

By Wayan in Logging 0 Comment

Here we demonstrate how to obtain the current level of the Logger instance. The log level will be inherited from the parent logger when the level is not set explicitly .

package org.kodejava.util.logging;

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

public class LoggerGetLevel {
    private static Logger logger = Logger.getLogger(LoggerGetLevel.class.getName());

    public static void main(String[] args) {
        LoggerGetLevel demo = new LoggerGetLevel();
        System.out.println("demo.getLevel(logger) = " + demo.getLevel(logger));

        logger.setLevel(Level.WARNING);
        System.out.println("demo.getLevel(logger) = " + demo.getLevel(logger));
    }

    public Level getLevel(Logger logger) {
        Level level = logger.getLevel();
        if (level == null && logger.getParent() != null) {
            level = logger.getParent().getLevel();
        }
        return level;
    }
}

How do I set the Logger log level?

By Wayan in Logging 0 Comment

In this example you see how we can change or set the Logger log level. The log level will tell the Logger which particular log message will be logged.

Logger will only record the log message if the level is equal or higher than the Logger level. For instance when the level set to Level.SEVERE, no message other than message logged with Logger.severe(String message) of Logger.log(Level level, String message) will be logged.

package org.kodejava.util.logging;

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

public class LogLevelSetting {
    // Obtains a Logger instance, it will create one if it is not already exist.
    private static final Logger logger = Logger.getLogger(LogLevelSetting.class.getName());

    public static void main(String[] args) {
        // Set the log level to Level.INFO, the severe message will be logged.
        logger.setLevel(Level.INFO);
        logger.severe("This message will be logged.");

        // Set the log level to Level.SEVERE, the warning message will not be
        // logged as Level.WARNING is smaller than Level.SEVERE
        logger.setLevel(Level.SEVERE);
        logger.warning("This message won't be logged.");

        // Turn of the log, no message will be logged.
        logger.setLevel(Level.OFF);
        logger.info("All log is turned off.");

        // Turn the logger back on, this will result all the corresponding
        // logger message below will be logged.
        logger.setLevel(Level.ALL);
        logger.info("Information message.");
        logger.warning("Warning message.");
        logger.severe("Severe message.");
    }
}

If we run the program above will see the following result displayed. In the output below we see that the "This message won't be logged." is not displayed.

Oct 08, 2021 7:12:53 AM org.kodejava.util.logging.LogLevelSetting main
SEVERE: This message will be logged.
Oct 08, 2021 7:12:54 AM org.kodejava.util.logging.LogLevelSetting main
INFO: Information message.
Oct 08, 2021 7:12:54 AM org.kodejava.util.logging.LogLevelSetting main
WARNING: Warning message.
Oct 08, 2021 7:12:54 AM org.kodejava.util.logging.LogLevelSetting main
SEVERE: Severe message.

How do I set a filter on a logger handler?

By Wayan in Logging 0 Comment

This example give you an example on how to set the Filter of a logger handler. In the code below we implement the Filter on the FileHandler to log only a Level.SEVERE message. Other log level will not be recorded to the file.

package org.kodejava.util.logging;

import java.util.logging.*;
import java.io.IOException;

public class LoggerFilter {
    public static void main(String[] args) {
        Logger logger = Logger.getLogger(LoggerFilter.class.getName());

        FileHandler handler = null;
        try {
            handler = new FileHandler("myapp.log");
            // The message will be recorded to the file When the 
            // LogRecord level is equals to Level.SEVERE
            handler.setFilter(record -> record.getLevel().equals(Level.SEVERE));
        } catch (IOException e) {
            logger.log(Level.SEVERE, "Fail to create logger handler", e);
        }

        logger.addHandler(handler);

        logger.info("Information message");
        logger.warning("Warning message");
        logger.severe("Severe message");
    }
}