Diagnostic Message

• It is usually a practice to generate messages within code for diagnosis (finding bugs…).
• The usual or naive approach is to use print statements.
  • We have to write these statements everywhere we need them and remove when we don’t need them
  • We have to enable/disable explicitly.
• Another Approach: Log diagnostic messages separately.
  • Logs are arranged hierarchically : We can choose the level of logging needed.
  • The messages has ability to be displayed in various formats.
  • The Logs can be processed by other codes(handlers) - Thus enabling to filter out uninteresting entries.
  • Logging can be controlled by a configuration file.

Logging

• Simplest: Call info() method of global logger:

  Logger.getGlobal().info("Edit->Copy menu item selected");

• This will print the following message:

  January 10,2022 10:12:15 PM LoggingImageViewer myFunction
  INFO: Edit-> Copy menu item selected.
  

• We can suppress logging by executing the following code

  	Logger.getGlobal().setLevel(Level.OFF);
  

• Can Create a Custom Logger.

  private static final Logger myLogger = Logger.getLogger("in.ac.iitm.onlinedegree");
  

Logging Levels

• Seven Logging Levels.

  SEVERE, WARNING, INFO, CONFIG, FINE, FINER, FINEST.

• By default, first three levels are logged.

  • Can set a different level: logger.setLevel(Level.FINE);

• Turn on all levels: logger.setLevel(Level.ALL);

• Turn off all logging: logger.setLevel(Level.OFF);

• Can also change logging properties through a configuration file.