• Some Data:
  • About 25% of maintenance expenditures are corrective (i.e., a result of defects found in the production environment) and preventive (i.e., a result of defects found in the development/testing environment)
• An Implication:
  • Design with maintenance (and support) in mind

• What is Logging?
  • A mechanism for recording or transmiting problems that arise at run time
• Users:
  • Developers
  • Field Service Engineers
  • Users
  • System Administrators

• Logger :
  • Used to log messages
• LogRecord :
  • An encapsulation of the information to be logged
• Handler :
  • Sends LogRecord objects to a variety of destinations including memory, output streams, consoles, files, and sockets
• Filter :
  • Provides fine-grained control over what gets logged
• Formatter :
  • Formats LogRecord objects

1. The application calls a method in a Logger object.
2. The Logger creates a LogRecord.
3. The Logger (perhaps after checking a log level and/or Filter) passes the LogRecord to a Handler.
4. The Handler uses a Formatter is used to format the LogRecord.

• Purpose:
  • Give a rough guide to the importance/urgency of an entry
• The Level Class:
  • Contains standard levels that range from SEVERE to FINEST

• Generic:
  • severe(String message)
  • warning(String message)
  • fine(String message)
  • finest(String message)
  • log(Level level, String message
• Specific:
  • entering()
  • exiting()
  • throwing()

• Handlers:
  • ConsoleHandler
  • FileHandler
  • SocketHandler
• Formatters:
  • SimpleFormatter
  • XMLFormatter

Logging Basics

javaexamples/logging/Driver.java

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


/**
 * An example that demonstrates how to use some of the
 * basic features of the java.util.logging package
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public class Driver
{


    /**
     * The entry point
     *
     * @Param args   The command line arguments (ignored)
     */
    public static void main(String[] args) throws Exception
    {
       FileHandler    handler;
       int            result;
       Logger         logger;
       


       // Get the default logger (alternatively, could create
       // one for this application)
       logger = Logger.getLogger(Logger.GLOBAL_LOGGER_NAME);


       // Create a FileHandler
       handler = new FileHandler("mylog.txt");   
       

       // Send logger output to our FileHandler
       logger.addHandler(handler);

       // Set the formatter
       handler.setFormatter(new SimpleFormatter());
        

       // Request that everything above this level gets logged.
       logger.setLevel(Level.FINE);

       // Log a simple INFO message.
       logger.log(Level.FINE, "Starting");

       try 
       {
          result = 1 / 0;
       } 
       catch (ArithmeticException ae) 
       {
          logger.log(Level.WARNING, "Trouble dividing", ae);
       }


       logger.log(Level.FINER, "Finished");
    }
}