Wrap configured ContextStorageProvider if available (#4359)

* Use SPI to search for other ContextStorageProviders and wrap them instead of using SentryOtelThreadLocalStorage

* Format code

* changelog

---------

Co-authored-by: Sentry Github Bot <bot+github-bot@sentry.io>

Author: adinauer

CHANGELOG.md

@@ -2,6 +2,14 @@
 
 ## Unreleased
 
+### Features
+
+- Wrap configured OpenTelemetry `ContextStorageProvider` if available ([#4359](https://github.com/getsentry/sentry-java/pull/4359))
+  - This is only relevant if you see `java.lang.IllegalStateException: Found multiple ContextStorageProvider. Set the io.opentelemetry.context.ContextStorageProvider property to the fully qualified class name of the provider to use. Falling back to default ContextStorage. Found providers: ...` 
+  - Set `-Dio.opentelemetry.context.contextStorageProvider=io.sentry.opentelemetry.SentryContextStorageProvider` on your `java` command
+  - Sentry will then wrap the other `ContextStorageProvider` that has been configured by loading it through SPI
+  - If no other `ContextStorageProvider` is available or there are problems loading it, we fall back to using `SentryOtelThreadLocalStorage`
+
 ### Fixes
 
 - Update profile chunk rate limit and client report ([#4353](https://github.com/getsentry/sentry-java/pull/4353))

sentry-opentelemetry/sentry-opentelemetry-bootstrap/src/main/java/io/sentry/opentelemetry/SentryContextStorageProvider.java

@@ -2,10 +2,32 @@
 
 import io.opentelemetry.context.ContextStorage;
 import io.opentelemetry.context.ContextStorageProvider;
+import java.util.Iterator;
+import java.util.ServiceLoader;
+import org.jetbrains.annotations.NotNull;
 
 public final class SentryContextStorageProvider implements ContextStorageProvider {
   @Override
   public ContextStorage get() {
-    return new SentryContextStorage(new SentryOtelThreadLocalStorage());
+    return new SentryContextStorage(findStorageToWrap());
+  }
+
+  private @NotNull ContextStorage findStorageToWrap() {
+    try {
+      ServiceLoader<ContextStorageProvider> serviceLoader =
+          ServiceLoader.load(ContextStorageProvider.class);
+      Iterator<ContextStorageProvider> iterator = serviceLoader.iterator();
+      while (iterator.hasNext()) {
+        ContextStorageProvider contextStorageProvider = iterator.next();
+        if (!(contextStorageProvider instanceof SentryContextStorageProvider)) {
+          return contextStorageProvider.get();
+        }
+      }
+    } catch (Throwable t) {
+      // ignore and use fallback
+    }
+
+    // using default / fallback storage
+    return new SentryOtelThreadLocalStorage();
   }
 }