Caused By: java.lang.NoClassDefFoundError: org/apache/log4j/Logger

Question

I\'ve got an interesting problem in which the org.apache.log4j.Logger class is not found during runtime. I\'m trying to get authorized and that is where it\'s failing:

Answer 1

You can use the following maven dependency in your pom file. Otherwise, you can download the following two jars from net and add it to your build path.

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.6.4</version>
</dependency>

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-log4j12</artifactId>
    <version>1.6.4</version>
</dependency>

This is copied from my working project. First make sure it is working in your project. Then you can change the versions to use any other(versions) compatible jars.

For AggCat, you can refer the POM file of the sample java application.

https://github.com/IntuitDeveloperRelations/IPP_Sample_Code/blob/master/CustomerAccountData/Java/AggCatSampleApplication/pom.xml

Thanks

Answer 2

With the suggestions @jhadesdev and the explanations from others, I've found the issue here.

After adding the code to see what was visible to the various class loaders I found this:

All versions of log4j Logger: 
  zip:<snip>war/WEB-INF/lib/log4j-1.2.17.jar!/org/apache/log4j/Logger.class

All versions of log4j visible from the classloader of the OAuthAuthorizer class: 
  zip:<snip>war/WEB-INF/lib/log4j-1.2.17.jar!/org/apache/log4j/Logger.class

All versions of XMLConfigurator: 
  jar:<snip>com.bea.core.bea.opensaml2_1.0.0.0_6-1-0-0.jar!/org/opensaml/xml/XMLConfigurator.class
  zip:<snip>war/WEB-INF/lib/ipp-java-aggcat-v1-devkit-1.0.2.jar!/org/opensaml/xml/XMLConfigurator.class
  zip:<snip>war/WEB-INF/lib/xmltooling-1.3.1.jar!/org/opensaml/xml/XMLConfigurator.class

All versions of XMLConfigurator visible from the classloader of the OAuthAuthorizer class: 
  jar:<snip>com.bea.core.bea.opensaml2_1.0.0.0_6-1-0-0.jar!/org/opensaml/xml/XMLConfigurator.class
  zip:<snip>war/WEB-INF/lib/ipp-java-aggcat-v1-devkit-1.0.2.jar!/org/opensaml/xml/XMLConfigurator.class
  zip:<snip>war/WEB-INF/lib/xmltooling-1.3.1.jar!/org/opensaml/xml/XMLConfigurator.class

I noticed that another version of XMLConfigurator was possibly getting picked up. I decompiled that class and found this at line 60 (where the error was in the original stack trace) private static final Logger log = Logger.getLogger(XMLConfigurator.class); and that class was importing from org.apache.log4j.Logger!

So it was this class that was being loaded and used. My fix was to rename the jar file that contained this file as I can't find where I explicitly or indirectly load it. Which may pose a problem when I actually deploy.

Thanks for all help and the much needed lesson on class loading.

Answer 3

Had the same problem, it was indeed caused by weblogic stupidly using its own opensaml implementation. To solve it, you have to tell it to load classes from WEB-INF/lib for this package in weblogic.xml:

    <prefer-application-packages>
        <package-name>org.opensaml.*</package-name>
    </prefer-application-packages>

maybe <prefer-web-inf-classes>true</prefer-web-inf-classes> would work too.

Answer 4

java.lang.ClassNotFoundException is indicate that class is not found in class path. it could be the version of log4j is not compatible. check for different log4j version.

Answer 5

During runtime your application is unable to find the jar.

Taken from this answer by Jared:

It is important to keep two different exceptions straight in our head in this case:

1. java.lang.ClassNotFoundException This an Exception, it indicates that the class was not found on the classpath. This indicates that we were trying to load the class definition, and the class did not exist on the classpath.

2. java.lang.NoClassDefFoundError This is Error, it indicates that the JVM looked in its internal class definition data structure for the definition of a class and did not find it. This is different than saying that it could not be loaded from the classpath. Usually this indicates that we previously attempted to load a class from the classpath, but it failed for some reason - now we're trying again, but we're not even going to try to load it, because we failed loading it earlier. The earlier failure could be a ClassNotFoundException or an ExceptionInInitializerError (indicating a failure in the static initialization block) or any number of other problems. The point is, a NoClassDefFoundError is not necessarily a classpath problem.

for similarities and differences

Answer 6

I had the same issue, for me this fixed the issue:
right click on the project ->maven -> update project