Dushyant-GitHub opened a new issue, #3504:
URL: https://github.com/apache/logging-log4j2/issues/3504
### Problem Description
Our web application, which runs in Tomcat 11 and Java 21, uses **SLF4J +
Logback** for logging. However, it allows dynamically importing extensions
along with JARs at runtime using the server **classloader**. One of these
extensions depends on `log4j-api-2.17.1.jar`, which is correctly present in the
classpath.
After deploying the extension, **calling a service that uses Log4j results
in the following error:**
`java.lang.NoClassDefFoundError: org/apache/logging/log4j/spi/ExtendedLogger`
However, other Log4j classes, such as `LogManager` and `Logger`, are loading
without issues.
### Environment Details
- **Application Type** : WAR-based Java web application
- **Application Server** : Apache Tomcat 11
- **Java Version** : 21
- **Logging Framework in Main App** : SLF4J with Logback
- **Extension Support** : Allows dynamic loading of JARs at runtime using
the server classloader
- **Problematic Dependency** : log4j-api-2.17.1.jar (used by an extension)
### Debugging Steps & Findings
1. Verified that `log4j-api-2.17.1.jar` is present in the classpath and
contains `org/apache/logging/log4j/spi/ExtendedLogger.class`.
2. Checked for multiple versions of `log4j-api` dependency in our
application. **Result** : Only one instance of log4j-api-2.17.1.jar is found.
3. Printed the class loaders for Log4j classes:
```
System.out.println(org.apache.logging.log4j.LogManager.class);
System.out.println(org.apache.logging.log4j.Logger.class);
System.out.println(org.apache.logging.log4j.spi.ExtendedLogger.class);
```
**Result**:
`LogManager` and `Logger` printed correctly.
`ExtendedLogger.class` throws `NoClassDefFoundError`.
### Additional Notes
- **Same application worked in Tomcat 9 without requiring a restart.**
- **Tomcat 11 requires a restart for `ExtendedLogger` to be found.**
- **After restarting Tomcat 11, everything works correctly.**
### Request for Help
We need guidance on :
- Why is `ExtendedLogger` missing, even though other Log4j classes load fine?
- Does Tomcat 11’s classloader affect Log4j differently compared to Tomcat 9?
- Are there additional configurations we should try in Tomcat 11?
Would appreciate any insights from the community!
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