How to link SLF4J with Log4J?

Question

I'm trying to set up a project using slf4j + log4j, but damn it just doesn't work ... I get an exception all the time:

Failed to instantiate SLF4J LoggerFactory Reported exception: java.lang.NoClassDefFoundError: org/apache/log4j/Level at org.slf4j.LoggerFactory.bind(LoggerFactory.java:129) at org.slf4j.LoggerFactory.performInitialization(LoggerFactory.java:108) at org.slf4j.LoggerFactory.getILoggerFactory(LoggerFactory.java:302) at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:276) at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:288) at TestLog.main(TestLog.java:9) Caused by: java.lang.ClassNotFoundException: org.apache.log4j.Level at java.net.URLClassLoader$1.run(URLClassLoader.java:372) at java.net.URLClassLoader$1.run(URLClassLoader.java:361) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:360) at java.lang.ClassLoader.loadClass(ClassLoader.java:424) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308) at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ... 6 more Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/log4j/Level at org.slf4j.LoggerFactory.bind(LoggerFactory.java:129) at org.slf4j.LoggerFactory.performInitialization(LoggerFactory.java:108) at org.slf4j.LoggerFactory.getILoggerFactory(LoggerFactory.java:302) at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:276) at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:288) at TestLog.main(TestLog.java:9) Caused by: java.lang.ClassNotFoundException: org.apache.log4j.Level at java.net.URLClassLoader$1.run(URLClassLoader.java:372) at java.net.URLClassLoader$1.run(URLClassLoader.java:361) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:360) at java.lang.ClassLoader.loadClass(ClassLoader.java:424) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308) at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ... 6 more 

I checked and the org.apache.log4j.Level class is present in my project in the section "Maven Dependencies> log4j-1.2.17.jar". So why can't the VM find it?

I have already tried the following options:

• slf4j-api + log4j
• slf4j-api + slf4j-log4j12
• slf4j-api + log4j
• slf4j-api + slf4j-log4j12 + log4j

None of the options worked :(

Here is my currnet pom.xml:

 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>org.sample</groupId> <artifactId>DBUnitSample</artifactId> <version>1.0</version> <dependencies> <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> <dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>1.2.17</version> </dependency> </dependencies> </project> 

Also, I noticed that when adding slf4j-log4j12 it adds log4j as a dependency as well as in the tree, so I assume adding log4j is obviously redundant here, but I added it anyway. Not lucky yet.

My main code is pretty simple:

 import org.slf4j.Logger; import org.slf4j.LoggerFactory; public class SampleDao { private static final Logger log = LoggerFactory.getLogger(SampleDao.class); public static void main(String[] args) { System.out.println("Hello"); log.info("Logged"); } } 

And my log4j.properties:

 log4j.rootLogger=DEBUG, STDOUT log4j.logger.deng=INFO log4j.appender.STDOUT=org.apache.log4j.ConsoleAppender log4j.appender.STDOUT.layout=org.apache.log4j.PatternLayout log4j.appender.STDOUT.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n 

Can someone please tell me what I am doing wrong? I already tried to find the answers to SO, but all the answers are mentioned to add the log4j dependency that I already added ... So I'm not sure what is wrong.

EDIT : Here is my whole project structure. I SampleDao R SampleDao and run it as a Java application. (At the moment, I also removed the dbunit dependency, to zero in the slf4j problem)

Answer 1

Try these dependencies

 <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-api</artifactId> <version>1.7.5</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>jcl-over-slf4j</artifactId> <version>1.7.5</version> <scope>runtime</scope> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-log4j12</artifactId> <version>1.7.5</version> <scope>runtime</scope> </dependency> 

Answer 2

Are you still getting an error if you run mvn compile exec:java -D"exec.mainClass"=SampleDao from the command line? After executing this command, I see the following on the command line: Maven 3.1.1 on my machine and your code:

 Hello INFO [SampleDao.main()] (SampleDao.java:9) - Logged 

So your POM and code seem to be great. There seems to be something wrong with the way you are trying to run the code.

Also note that the following simplified configuration should work:

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

You will need to specify a specific version of Log4j if the POM has other dependencies that add different versions of Log4j to the project.

Answer 3

Add the dependency below:

 <dependency> <groupId>ch.qos.logback</groupId> <artifactId>logback-core</artifactId> <version>${logback.version}</version> </dependency> 

Answer 4

I met the same error as you. I solved my problem according to the following two sentences. Hope this helps.

1. Modify your POM file:

 <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-api</artifactId> <version>1.7.2</version> </dependency> <dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>1.2.12</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-log4j12</artifactId> <version>1.7.2</version> </dependency> 

2. Add the jar to your startup script

 java -cp ./lib/log-producer-1.0.4-SNAPSHOT.jar:./lib/slf4j-log4j12-1.7.2.jar:./lib/slf4j-api-1.7.2.jar:./lib/log4j-1.2.12.jar cn.tiakon.core.Bootstrap