nielsm5 opened a new issue, #4028:
URL: https://github.com/apache/logging-log4j2/issues/4028
## Description
There is a loadClass method in the `ThrowableExtendedStackTraceRenderer`.
```java
private static Class<?> loadClass(final ClassLoader loader, final
String className) {
for (final ClassLoadingStrategy strategy :
CLASS_LOADING_STRATEGIES) {
try {
final Class<?> clazz = strategy.run(loader, className);
if (clazz != null) {
return clazz;
}
} catch (final Exception ignored) {
// Do nothing
}
}
return null;
}
```
Which when unable to lookup the given class, should do nothing. But
Classloaders throw NoClassDefFoundError which is an `Error` and thus not
caught. This breaks log4j2, causing our app to log a beautify 'log4j2 cannot
log something exception` and not the actual message+stacktrace it should log!
## Configuration
**Version:** 2.25.3
**Operating system:** Windows, unrelated to this.
**JDK:** 21 and 25, also unrelated.
## Logs
```
2026-01-21T13:27:17.646390600Z main ERROR An exception occurred processing
Appender application-log-appender
org.apache.logging.log4j.core.appender.AppenderLoggingException:
java.lang.NoClassDefFoundError: org/frankframework/core/IPushingListener
at
org.apache.logging.log4j.core.config.AppenderControl.tryCallAppender(AppenderControl.java:164)
at
org.apache.logging.log4j.core.config.AppenderControl.callAppender0(AppenderControl.java:133)
at
org.apache.logging.log4j.core.config.AppenderControl.callAppenderPreventRecursion(AppenderControl.java:124)
at
org.apache.logging.log4j.core.config.AppenderControl.callAppender(AppenderControl.java:88)
at
org.apache.logging.log4j.core.appender.routing.RoutingAppender.append(RoutingAppender.java:256)
at
org.apache.logging.log4j.core.config.AppenderControl.tryCallAppender(AppenderControl.java:160)
at
org.apache.logging.log4j.core.config.AppenderControl.callAppender0(AppenderControl.java:133)
at
org.apache.logging.log4j.core.config.AppenderControl.callAppenderPreventRecursion(AppenderControl.java:124)
at
org.apache.logging.log4j.core.config.AppenderControl.callAppender(AppenderControl.java:88)
at
org.apache.logging.log4j.core.config.LoggerConfig.callAppenders(LoggerConfig.java:711)
at
org.apache.logging.log4j.core.config.LoggerConfig.processLogEvent(LoggerConfig.java:669)
at
org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:645)
at
org.apache.logging.log4j.core.config.LoggerConfig.logParent(LoggerConfig.java:702)
at
org.apache.logging.log4j.core.config.LoggerConfig.processLogEvent(LoggerConfig.java:671)
at
org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:645)
at
org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:589)
at
org.apache.logging.log4j.core.config.DefaultReliabilityStrategy.log(DefaultReliabilityStrategy.java:73)
at org.apache.logging.log4j.core.Logger.log(Logger.java:187)
at
org.apache.logging.log4j.spi.AbstractLogger.tryLogMessage(AbstractLogger.java:2970)
at
org.apache.logging.log4j.spi.AbstractLogger.logMessageTrackRecursion(AbstractLogger.java:2922)
at
org.apache.logging.log4j.spi.AbstractLogger.logMessageSafely(AbstractLogger.java:2904)
at
org.apache.logging.log4j.spi.AbstractLogger.logMessage(AbstractLogger.java:2648)
at
org.apache.logging.log4j.spi.AbstractLogger.logIfEnabled(AbstractLogger.java:2587)
at
org.apache.logging.log4j.spi.AbstractLogger.error(AbstractLogger.java:824)
.. many many more
```
## Reproduction
Very difficult, requires custom classloaders.
https://github.com/frankframework/frankframework/issues/10312
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