SLF4J Explained........

SLF4J Logging

1. SLF4J Explained

2. Why need logging? Format of java logs Format of messages w hat to log in java which   logging level to use  for which kind of messages

3. Why SLF4J ? Jakarta Commons Logging (JCL) java.util.logging . - Same problem domain -Well-established library So why do we re-invent the wheel? Because details of implementation matter. A simpler implementation is preferable to more complex variant even if the latter offers other advantages .

4. What is SLF4J Sl4j-Simple Logging Façade for Java slf4j is a facade, not an implementation. Log4J was initially created by Ceki Gülcü . After Log4J Ceki created SLF4J, so I guess he put everything he learned from Log4J into SLF4J . SLF4J provides a nice way of creating short and easy to read logging statements in the code, that have only minor resource consumption if logging is turned off . String message = "Could not find our DataSource in WAT Database."; logger .error ("*** " , message ); logger.debug ("{}", complexObject ); logger.debug ("Info : x = {}, y = {}, str = {}", new Object[]{ info.getX (), info.getY (), infos.getStr ()});

5. competitors . How does it work?

6. SLF4J debug(String msg ); debug(String format, Object arg ); debug(String format, Object arg1, Object arg2);           debug(String msg , Throwable t);

7. Sample Code 1: import org.slf4j.Logger; 2: import org.slf4j.LoggerFactory; 3: 4: public class Wombat { 5: 6 : final Logger logger = LoggerFactory.getLogger ( Wombat.class ); 7: Integer t; 8: Integer oldT ; 9: 10: public void setTemperature ( Integer temperature ) { 11: 12: oldT = t; 13: t = temperature ; 14: 15 : logger.debug (" Temperature set to {}. Old temperature was {}.", t, oldT ) ; 16: 17: if( temperature.intValue () > 50) { 18: logger.info(" Temperature has risen above 50 degrees ."); 19: } 20: } 21: }

8. Parameterized logging inefficient syle : logger.debug ("Hello "+ name ); old style (inefficient): if( logger.isDebugEnabled ()) { logger.debug ("Hello "+ name ); } new style (efficient): logger.debug ("Hello {} ", name );

9. How to setup SLF4J and LOGBack in a web app - fast import the following libraries to your WEB-INF/lib folder: WEB-INF lib logback-classic.x.x.x.jar logback-core.x.x.x.jar slf4j-api-x.x.x.jar TOMCAT ( { catlina -home}/lib logback-classic.1.0.9.jar logback-core.1.0.9.jar slf4j-api-1.0.9.jar

10. SLF4J explained.. Object entry = new SomeObject (); if( logger.isDebugEnabled ()) {   logger.debug ("Entry number: " + i + " is " + String.valueOf (entry[ i ])); } logger.debug ("The entry is {}.", entry);

11. Logback.xml <?xml version= "1.0" encoding="UTF-8"?> <configuration> < appender name= "FILE" class=" ch.qos.logback.core.FileAppender "> <file>c:\testlog1.log</file> <layout class= " ch.qos.logback.classic.PatternLayout "> <Pattern>%date %level [%thread] %logger{10} [%file:%line] % msg%n </Pattern> </layout> </ appender > <root> <level value= "debug" /> < appender -ref ref= "FILE" /> </root> </configuration>

12. Other Supported Features MDC Markers

13. Marker????? Marker API The Marker allow essentially to associate tags to logs. This tags enable the different appenders to take only some logs. Lets imagine an appender who write the log using encryption and that must only be used on logs marked as confidentials . The Marker enable us to implement that.

14. Marker API < appender name="CRYPTED" class=" CryptAppender "> <layout class=" ch.qos.logback.classic.html.HTMLLayout "> <pattern>%date%-5level%logger%msg</pattern> < throwableRenderer class=" ch.qos.logback.classic.html.DefaultThrowableRenderer " /> </layout> <evaluator class=" ch.qos.logback.classic.boolex.OnMarkerEvaluator "> < marker>CONFIDENTIAL</marker> </evaluator> </ appender >

15. Marker API Marker confidentialMarker = MarkerFactory.getMarker (" CONFIDENTIL"); logger.error ( confidentialMarker , “ very vconfidentiel !");

16. MDC A simple map (key-value set) maintained by the logging framework. In that map, the application can put some key-value couple that could be used to add some informations in the logs.

17. MDC --Explained MDC.put (“user", ‘Marriot Hotel"); MDC.put (“” Location", “status"); % X{user} % X{ device id} - % m%n logger.info (“ logDate {}", logdate ); logger.info (“ deviceID {}", status); Marriot Hotel- Log Date Location - Atlanta

18. Conclusion It’s really powerful, but remains really simple to use and the style is the same as the other existing logging systems . Simplicity is powerful. -- Evan Williams

19. References http:// www.slf4j.org/ http://parleys.com/play/514892260364bc17fc56be83/chapter0/about