How do I create a custom logger Formatter?

By I Wayan Saryada in Logging 5 Comments

To create a custom Formatter we need to extend the java.util.logging.Formatter abstract class and implements the format(LogRecord) method. In the method then we can format the log message stored in the LogRecord to match our need.

The java.util.logging.Formatter class also have the getHead(Handler) and getTail(Handler) which can be overridden to add a head and a tail to our log message.

package org.kodejava.util.logging;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.logging.*;

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

        MyFormatter formatter = new MyFormatter();
        ConsoleHandler handler = new ConsoleHandler();
        handler.setFormatter(formatter);

        logger.addHandler(handler);
        logger.info("Example of creating custom formatter.");
        logger.warning("A warning message.");
        logger.severe("A severe message.");
    }
}

class MyFormatter extends Formatter {
    // Create a DateFormat to format the logger timestamp.
    private static final DateFormat df = new SimpleDateFormat("dd/MM/yyyy hh:mm:ss.SSS");

    public String format(LogRecord record) {
        StringBuilder builder = new StringBuilder(1000);
        builder.append(df.format(new Date(record.getMillis()))).append(" - ");
        builder.append("[").append(record.getSourceClassName()).append(".");
        builder.append(record.getSourceMethodName()).append("] - ");
        builder.append("[").append(record.getLevel()).append("] - ");
        builder.append(formatMessage(record));
        builder.append("\n");
        return builder.toString();
    }

    public String getHead(Handler h) {
        return super.getHead(h);
    }

    public String getTail(Handler h) {
        return super.getTail(h);
    }
}

Below is an output produced by the custom formatter above.

08/10/2021 07:55:55.153 - [org.kodejava.util.logging.LogCustomFormatter.main] - [INFO] - Example of creating custom formatter.
08/10/2021 07:55:55.164 - [org.kodejava.util.logging.LogCustomFormatter.main] - [WARNING] - A warning message.
08/10/2021 07:55:55.164 - [org.kodejava.util.logging.LogCustomFormatter.main] - [SEVERE] - A severe message.

How do I prevent the logger send log messages to its parent logger?

By I Wayan Saryada in Logging 0 Comment

To prevent log records being forwarded to the logger’s parent handlers we can set false the useParentHandlers field using the Logger.setUserParentHandlers(boolean useParentHandlers) method.

package org.kodejava.util.logging;

import java.util.logging.Logger;
import java.util.logging.ConsoleHandler;

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

        // Do not forward any log messages the logger parent handlers.
        logger.setUseParentHandlers(false);

        // Specify a ConsoleHandler for this logger instance.
        logger.addHandler(new ConsoleHandler());
        logger.info("Logging an information message.");
    }
}

How do I set the formatter of logger handlers?

By I Wayan Saryada 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 I Wayan Saryada 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 I Wayan Saryada 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;
    }
}