Logging to a File - Using a FileHandler

Java has a built in logging mechanism. This mechanism was adding to provide logging functionality to the base Java libraries. This removes external dependencies from your project, and allows you to use logging within the base framework.

Log4J has an incredible amount functionality, but requires that you add the framework to your project and its dependencies. There is also configuration required up front to use the logging.

The default logging mechanism is very easy to use. We simply create a Logger instance from the static class. Using it is as simple as calling Logger.getAnonymousLogger();. This allows you to create an anonymous logger which is a console logger. There is no default mechanism for logging to the file system. This accomplished by using a FileHandler.

A simple sample implementation is located below. I have please note the comments. The NetBeans project is located here: ExampleLogger.zip

ExampleLogger.java

---

/*
 * Copyright 2011 John Yeary <jyeary@bluelotussoftware.com>.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.bluelotussoftware.example;

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

/**
 *
 * @author John Yeary <jyeary@bluelotussoftware.com>
 * @version 1.0
 */
public class LoggerExample {

    private static final Logger logger = Logger.getLogger(LoggerExample.class.getName());
    private FileHandler fileHandler;

    public LoggerExample() {
        /*
         * This is one option using the FileHandler in the constructor
         * for the class. This will work if we need to instantiate
         * the class before use. In the case of a class where the main()
         * method is located we should consider a separate case in
         * the main method to initialize the handler. (See below)
         */
        addFileHandler(logger);
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        logger.info("main() method called.");

        /*
         * Instantiating the class with actually create two
         * FileHandlers.
         */
        LoggerExample le = new LoggerExample();

        /*
         * Anonymous inner class method for adding a FileHandler
         * in main() method.
         */
        try {
            logger.info("Adding FileHandler");
            logger.addHandler(new FileHandler(LoggerExample.class.getName()
                    + ".main.log"));
            logger.info("Added FileHandler to Logger");
        } catch (IOException ex) {
            logger.log(Level.SEVERE, null, ex);
        } catch (SecurityException ex) {
            logger.log(Level.SEVERE, null, ex);
        }

        // Example logging.
        logger.info("Logging for fun and profit");
        logger.fine("Fine...");
        logger.finer("Finer...");
        logger.finest("Finest...");
        logger.warning("Warning...");
        logger.severe("Severe...");
        logger.info("Logging complete.");
    }

    /**
     * Add a <code>FileHandler</code> to the provided <code>Logger</code>.
     * @param logger <code>Logger</code> to add <code>FileHandler</code>.
     */
    private void addFileHandler(Logger logger) {
        try {
            fileHandler = new FileHandler(LoggerExample.class.getName() + ".log");
        } catch (IOException ex) {
            logger.log(Level.SEVERE, null, ex);
        } catch (SecurityException ex) {
            logger.log(Level.SEVERE, null, ex);
        }
        logger.addHandler(fileHandler);
    }
}