How to get SLF4J "Hello World" working with log4j?

Question

The "Hello World" example from SLF4J is not working for me. I guess this is because I added slf4j-log4 to my classpath. Should I configure log4j directly for the hello world to work?

log4j:WARN No appenders could be found for logger (HelloWorld). log4j:WARN Please initialize the log4j system properly. log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info. 

Update: I added log4j initialization, and it still doesn't work:

public static void main(String[] params) {         org.apache.log4j.Logger.getRootLogger().addAppender(new ConsoleAppender());         Logger logger = org.slf4j.LoggerFactory.getLogger(TestBase.class);         logger.info("Hello World");     } 

And I'm getting:

log4j:ERROR No output stream or file set for the appender named [null]. 

Answer 1

If you want to use slf4j simple, you need these jar files on your classpath:

• slf4j-api-1.6.1.jar
• slf4j-simple-1.6.1.jar

If you want to use slf4j and log4j, you need these jar files on your classpath:

• slf4j-api-1.6.1.jar
• slf4j-log4j12-1.6.1.jar
• log4j-1.2.16.jar

No more, no less. Using slf4j simple, you'll get basic logging to your console at INFO level or higher. Using log4j, you must configure it accordingly.

Answer 2

Following is an example. You can see the details http://jkssweetlife.com/configure-slf4j-working-various-logging-frameworks/ and download the full codes here.

• Add following dependency to your pom if you are using maven, otherwise, just download the jar files and put on your classpath

  <dependency>     <groupId>org.slf4j</groupId>     <artifactId>slf4j-api</artifactId>     <version>1.7.7</version> </dependency>  <dependency>     <groupId>org.slf4j</groupId>     <artifactId>slf4j-log4j12</artifactId>     <version>1.7.7</version> </dependency> 

• Configure log4j.properties

  log4j.rootLogger=TRACE, stdout log4j.appender.stdout=org.apache.log4j.ConsoleAppender log4j.appender.stdout.Target=System.out log4j.appender.stdout.layout=org.apache.log4j.PatternLayout log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd'T'HH:mm:ss.SSS} %-5p [%c] - %m%n 

• Java example

  public class Slf4jExample {     public static void main(String[] args) {          Logger logger = LoggerFactory.getLogger(Slf4jExample.class);          final String message = "Hello logging!";         logger.trace(message);         logger.debug(message);         logger.info(message);         logger.warn(message);         logger.error(message);     } }