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Introduction

In Java, application activity can be captured using logging. Logging is useful for many purposes such as:

Keeping track of unusual events or potential program errors

Obtaining detailed information about what is happening in the application

Recording website visits on web servers (e.g., IP address, time of visit, pages accessed)

Storing additional details during development and testing for debugging purposes

Logging Levels

A log message's importance is determined by its log level (or log severity). Log levels make it easy to categorize and filter log events. If used properly, you can quickly identify the severity of events by just checking the log level.

Severe – Indicates critical failures (e.g., database unavailability, out of memory). Immediate action required.

Warning – Potential issues (e.g., incorrect credentials, invalid input).

Info – General information about significant application state changes (used by admins/advanced users).

Config – Configuration details such as CPU type, disk size, or memory usage.

Fine – Important but less severe messages.

Finer – Detailed tracing messages for debugging.

Finest – Extremely detailed tracing information.

OFF – Integer.MAX_VALUE, used to disable all logging.

ALL – Integer.MIN_VALUE, used to capture everything.

Java’s Log System

Java provides a Log Manager that controls the configuration of the logging system and manages logger objects. A single global instance of the LogManager class is responsible for handling log files. You can access it using the static method getLogManager().

Example Code

import java.util.logging.*;

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

    public static void main(String[] args) {
        logger.setLevel(Level.ALL);

        logger.severe("Severe message - critical issue!");
        logger.warning("Warning message - potential problem.");
        logger.info("Info message - general application info.");
        logger.config("Config message - system confi