Log4j2 : NoClassDefFoundError : LogManager

Question

I was trying out Log4j2 so I created a Java project in eclipse. My code is same as Log4j2 Manual Automatic Configuration part. I have added log4j-api-2.17.2.jar and log4j-core-2.17.2.jar in the classpath. When I run the application I get following error

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/logging/log4j/LogManager
    at demo.one.MainClass.<clinit>(MainClass.java:8)
Caused by: java.lang.ClassNotFoundException: org.apache.logging.log4j.LogManager
    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
    at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)

I have checked some related questions but didn't find those useful.

Is `org.apache.logging.log4j.LogManager` present in your project (including libraries)? — Thorbjørn Ravn Andersen, Jul 21 '22 at 12:13
Don't understand your question properly. I have the api and core jar files in referenced library. — Mahmud Mridul, Jul 21 '22 at 17:57
How exactly do you run your code? Please provide full command lines? (Reason is that this can be explained by an incorrect classpath argument) — Thorbjørn Ravn Andersen, Jul 21 '22 at 19:36
I ran the code from eclipse. I selected "Run as Java Application" and chose MyApp class. — Mahmud Mridul, Jul 23 '22 at 07:18
LogManager should be in log4j-api, so I would have a closer look at how exactly you added the jar files to the classpath. You might have missed a step. — Thorbjørn Ravn Andersen, Jul 23 '22 at 14:28
So here was the problem, both jar files were in .classpath file as "module" because I added them as modulepath in eclipse. But jars have to added as "classpath". So in .classpath file jars should look like below: ``` ``` — Mahmud Mridul, Jul 26 '22 at 04:27

score 0 · Answer 1 · answered Jul 21 '22 at 12:59

In case you use maven, make sure to include Log4j core to the project:

<!-- https://mvnrepository.com/artifact/org.apache.logging.log4j/log4j-core -->
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-core</artifactId>
    <version>2.18.0</version>
</dependency>

score 0 · Answer 2 · answered Jul 21 '22 at 17:50

0

Since, it's a NoClassDefFoundError, that means your JRE is not able to find out the necessary jar(class) artifact holding definition for org.apache.logging.log4j.LogManager. Look for differences between build and runtime classpaths.

answered Jul 21 '22 at 17:50

Jaraws

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score 0 · Answer 3 · answered May 26 '23 at 02:34

0

how did u run the code? If from terminal, you might want to add maven-shade-plugin https://maven.apache.org/plugins/maven-shade-plugin/examples/executable-jar.html

answered May 26 '23 at 02:34

keepscoding

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Please don't just link to a tool or library. Instead, also include details about what it does, how it addresses the OP's question, and ideally how to use it to solve the specifics of the case. **Would you kindly [edit] your answer to include this information?** – Jeremy Caney May 26 '23 at 02:39
Check also [this answer](https://stackoverflow.com/a/76015329/11748454) for the 3 resource transformers required by Log4j 2.x. – Piotr P. Karwasz May 26 '23 at 06:52

Log4j2 : NoClassDefFoundError : LogManager

3 Answers3