Fix NoClassDefFoundError

✅ Solution

The NoClassDefFoundError in XGBoost, especially related to JNI, often indicates that the XGBoost native library (e.g., xgboost4j.dll, libxgboost4j.so) is missing from the Java classpath or is not accessible by the JVM. Ensure that the XGBoost native library corresponding to your system architecture is correctly placed in a directory included in your java.library.path or is bundled within your application's resources, and is loaded before XGBoost classes are initialized. Specifically verify XGBoostJNI is accessible to the JVM at runtime when the Booster object is loaded.