java.util.logging

1. Logger and Level

package com.javacodegeeks.corejava.util.logging;

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

public class LoggerExample {

	private static final Logger LOGGER = Logger.getLogger(LoggerExample.class.getName());
	public static void main(String[] args) throws SecurityException, IOException {

		LOGGER.info("Logger Name: "+LOGGER.getName());
		
		LOGGER.warning("Can cause ArrayIndexOutOfBoundsException");
		
		//An array of size 3
		int []a = {1,2,3};
		int index = 4;
		LOGGER.config("index is set to "+index);
		
		try{
			System.out.println(a[index]);
		}catch(ArrayIndexOutOfBoundsException ex){
			LOGGER.log(Level.SEVERE, "Exception occur", ex);
		}
		

	}

}

2.Handler

package com.javacodegeeks.corejava.util.logging;

import java.io.IOException;
import java.util.logging.ConsoleHandler;
import java.util.logging.FileHandler;
import java.util.logging.Handler;
import java.util.logging.Level;
import java.util.logging.Logger;

public class HandlerExample {

	private static final Logger LOGGER = Logger.getLogger(LoggerExample.class
			.getName());

	public static void main(String[] args) {

		Handler consoleHandler = null;
		Handler fileHandler = null;
		try {
			// Creating consoleHandler and fileHandler
			consoleHandler = new ConsoleHandler();
			fileHandler = new FileHandler("./javacodegeeks.log");

			// Assigning handlers to LOGGER object
			LOGGER.addHandler(consoleHandler);
			LOGGER.addHandler(fileHandler);

			// Setting levels to handlers and LOGGER
			consoleHandler.setLevel(Level.ALL);
			fileHandler.setLevel(Level.ALL);
			LOGGER.setLevel(Level.ALL);

			LOGGER.config("Configuration done.");

			// Console handler removed
			LOGGER.removeHandler(consoleHandler);

			LOGGER.log(Level.FINE, "Finer logged");
		} catch (IOException exception) {
			LOGGER.log(Level.SEVERE, "Error occur in FileHandler.", exception);
		}

		LOGGER.finer("Finest example on LOGGER handler completed.");

	}

}

3. Formatter

package com.javacodegeeks.corejava.util.logging;

import java.io.IOException;
import java.util.logging.Formatter;
import java.util.logging.FileHandler;
import java.util.logging.Handler;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.logging.SimpleFormatter;

public class FormatterExample {

	private static final Logger LOGGER = Logger.getLogger(LoggerExample.class
			.getName());

	public static void main(String[] args) {

		Handler fileHandler = null;
		Formatter simpleFormatter = null;
		try {

			// Creating FileHandler
			fileHandler = new FileHandler("./javacodegeeks.formatter.log");

			// Creating SimpleFormatter
			simpleFormatter = new SimpleFormatter();

			// Assigning handler to logger
			LOGGER.addHandler(fileHandler);

			// Logging message of Level info (this should be publish in the
			// default format i.e. XMLFormat)
			LOGGER.info("Finnest message: Logger with DEFAULT FORMATTER");

			// Setting formatter to the handler
			fileHandler.setFormatter(simpleFormatter);

			// Setting Level to ALL
			fileHandler.setLevel(Level.ALL);
			LOGGER.setLevel(Level.ALL);

			// Logging message of Level finest (this should be publish in the
			// simple format)
			LOGGER.finest("Finnest message: Logger with SIMPLE FORMATTER");
		} catch (IOException exception) {
			LOGGER.log(Level.SEVERE, "Error occur in FileHandler.", exception);
		}
	}

}

4.Filter

package com.javacodegeeks.corejava.util.logging;

import java.util.logging.Filter;
import java.util.logging.LogRecord;
import java.util.logging.Logger;

public class FilterExample implements Filter{

	private static final Logger LOGGER = Logger.getLogger(LoggerExample.class.getName());
	public static void main(String[] args) {
		//Setting filter FilterExample
		LOGGER.setFilter(new FilterExample());
		//Since this message string does not contain the word important. Despite of being the Level SEVERE this will be ignored
		LOGGER.severe("This is SEVERE message");
		//This will get published
		LOGGER.warning("This is important warning message");

	}
	
	// This method will return true only if the LogRecord object contains the message which contains the word important 
	@Override
	public boolean isLoggable(LogRecord record) {
		if(record == null)
			return false;
		
		String message = record.getMessage()==null?"":record.getMessage();
		
		if(message.contains("important"))
			return true;
		
		return false;
	}

}

5.Configuration

package com.javacodegeeks.corejava.util.logging;

import java.io.FileInputStream;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.LogManager;
import java.util.logging.Logger;

public class ConfigurationExample {

	private static final LogManager logManager = LogManager.getLogManager();
	private static final Logger LOGGER = Logger.getLogger("confLogger");
	static{
		try {
			logManager.readConfiguration(new FileInputStream("./javacodegeeks.properties"));
		} catch (IOException exception) {
			LOGGER.log(Level.SEVERE, "Error in loading configuration",exception);
		}
	}
	public static void main(String[] args) {
		LOGGER.fine("Fine message logged");
	}
}

javacodegeeks.properties

handlers=java.util.logging.ConsoleHandler
.level=ALL
java.util.logging.ConsoleHandler.level=ALL
java.util.logging.ConsoleHandler.formatter=java.util.logging.SimpleFormatter
confLogger.level=ALL