Log4j 2.0 - Some important features

Log4j’s latest 2.0 version has been recently released. Following are few of the important and very useful features of Log4j-2.0:

1.       Supports parameter substitution (same as slf4j)

For example:

   LOGGER.info (“User Id is { } and User Email is { }”, userId, userEmail);

2.       Flow Tracing:

To print the entry and exit of a method.

Example:

  public String getUserEmail(int userId) {

    logger.entry(userId);

    User user = UserDao.getUser(userId)

    String email = user.getEmail();

    return logger.exit(email);

  }

  This method will log following messages:

    19:08:07.061 TRACE com.class.MyClass 10 getUserEmail -  entry parms(1)

    19:08:07.061 TRACE com.class.MyClass 13 getUserEmail -  exit with (User.Email@gmail.com)

3.       Markers:

To log some special messages.

For example:

 public class MyApp {

   private Logger logger = LogManager.getLogger(MyApp.class.getName());

   private static final Marker QUERY_MARKER = MarkerManager.getMarker("SQL");

   public String doQuery(String table) {

     logger.entry(param);

     logger.debug(QUERY_MARKER, "SELECT * FROM {}", table);

     return logger.exit();

   }

} 

4.       Messages:

Very useful to standardize the format of an application’s log messages.

Example:

            logger.info("User {} has logged in using id {}", username, userId);        

      The above log message can be standardized by implementing a class ‘LoggedInMessage’ implementing ‘Message’ interface.

            logger.info(new LoggedInMessage(userName, userId)); 

                    (‘getFormattedMessage’ method of ‘Message’ interface is used to log the message string.)

Some more important types of messages are ThreadDumpMessage, TimestampMessage, MapMessage and few more.

5.       Plug-ins:

Log4j 2 uses a Plugin system that makes it extremely easy to extend the framework by adding new Appenders, Filters, Layouts, Lookups, and Pattern Converters without requiring any changes to Log4j.           

-          Sarang Anajwala