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

User · Answer

I had the same problem   I called my own custom logger in the log4j properties file from code when using log4j api directly   If you are using the slf4j api calls  you are probably using the default root logger so you must configure that to be associated with an appender in the log4j properties           Set root logger level to DEBUG and its only appender to A1      log4j rootLogger DEBUG  A1        A1 is set to be a ConsoleAppender      log4j appender A1 org apache log4j ConsoleAppender

User · Answer

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   lt dependency gt       lt groupId gt org slf4j lt  groupId gt       lt artifactId gt slf4j-api lt  artifactId gt       lt version gt 1 7 7 lt  version gt   lt  dependency gt    lt dependency gt       lt groupId gt org slf4j lt  groupId gt       lt artifactId gt slf4j-log4j12 lt  artifactId gt       lt version gt 1 7 7 lt  version gt   lt  dependency gt   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

User · Answer

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

User · Answer

you need to add 3 dependency   API  API implementation   log4j dependency   Add also this   lt dependency gt       lt groupId gt org apache logging log4j lt  groupId gt       lt artifactId gt log4j-core lt  artifactId gt       lt version gt 2 5 lt  version gt   lt  dependency gt     And to see log in command line   set log4j properties     Root logger option log4j rootLogger INFO  file  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 HH mm ss   -5p  c 1   L -  m n   And to see log in file    set log4j properties    Direct log messages to a log file log4j appender file org apache log4j RollingFileAppender log4j appender file File   logs logging log log4j appender file MaxFileSize 10MB log4j appender file MaxBackupIndex 10 log4j appender file layout org apache log4j PatternLayout log4j appender file layout ConversionPattern  d yyyy-MM-dd HH mm ss   -5p  c 1   L -  m n

User · Answer

Here a working example to use slf4j as fa  ade with log4j in the backend  pom xml  lt project xmlns  quot http   maven apache org POM 4 0 0 quot      xmlns xsi  quot http   www w3 org 2001 XMLSchema-instance quot      xsi schemaLocation  quot http   maven apache org POM 4 0 0 https   maven apache org xsd maven-4 0 0 xsd quot  gt       lt modelVersion gt 4 0 0 lt  modelVersion gt       lt groupId gt xxx lt  groupId gt       lt artifactId gt xxx lt  artifactId gt       lt version gt 0 0 1-SNAPSHOT lt  version gt        lt dependencies gt           lt  -- https   mvnrepository com artifact org slf4j slf4j-api -- gt           lt dependency gt               lt groupId gt org slf4j lt  groupId gt               lt artifactId gt slf4j-api lt  artifactId gt               lt version gt 1 7 30 lt  version gt           lt  dependency gt           lt  -- https   mvnrepository com artifact org slf4j slf4j-log4j12 -- gt           lt dependency gt               lt groupId gt org slf4j lt  groupId gt               lt artifactId gt slf4j-log4j12 lt  artifactId gt               lt version gt 1 7 30 lt  version gt           lt  dependency gt           lt  -- https   mvnrepository com artifact org apache logging log4j log4j-core -- gt           lt dependency gt               lt groupId gt org apache logging log4j lt  groupId gt               lt artifactId gt log4j-core lt  artifactId gt               lt version gt 2 13 3 lt  version gt           lt  dependency gt       lt  dependencies gt   lt  project gt   src main resources log4j properties   Root logger option log4j rootLogger DEBUG  stdout    Direct log messages to 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 HH mm ss   -5p  c 1   L -  m n  src main java Main java import org slf4j Logger  import org slf4j LoggerFactory   public class Main       private static final Logger logger   LoggerFactory getLogger Main class                   Default private constructor              private Main                           Main method                 param args Arguments passed to the execution of the application             public static void main final String   args            logger info  quot Message to log quot

[java] How to get SLF4J "Hello World" working with log4j?

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