Use thread context classloader when available (#4320)

* Use thread context classloader when available

* ./gradlew spotlessApply

* changelog

* Update CHANGELOG.md

---------

Co-authored-by: lcian <lorenzo.cian@sentry.io>
Co-authored-by: Lorenzo Cian <cian.lorenzo@gmail.com>

Author: acmi

CHANGELOG.md

@@ -1,5 +1,12 @@
 # Changelog
 
+## Unreleased
+
+### Fixes
+
+- Use thread context classloader when available ([#4320](https://github.com/getsentry/sentry-java/pull/4320))
+  - This ensures correct resource loading in environments like Spring Boot where the thread context classloader is used for resource loading.
+
 ## 8.7.0
 
 ### Features

sentry/src/main/java/io/sentry/util/ClassLoaderUtils.java

@@ -8,6 +8,13 @@ public final class ClassLoaderUtils {
   public static @NotNull ClassLoader classLoaderOrDefault(final @Nullable ClassLoader classLoader) {
     // bootstrap classloader is represented as null, so using system classloader instead
     if (classLoader == null) {
+      // try thread context classloader
+      final @Nullable ClassLoader contextClassLoader =
+          Thread.currentThread().getContextClassLoader();
+      if (contextClassLoader != null) {
+        return contextClassLoader;
+      }
+      // fallback to system classloader
       return ClassLoader.getSystemClassLoader();
     } else {
       return classLoader;