add listener

src/main/java/rocks/inspectit/gepard/agent/transformation/InspectitListener.java

@@ -0,0 +1,49 @@
+package rocks.inspectit.gepard.agent.transformation;
+
+import net.bytebuddy.agent.builder.AgentBuilder;
+import net.bytebuddy.description.type.TypeDescription;
+import net.bytebuddy.dynamic.DynamicType;
+import net.bytebuddy.utility.JavaModule;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Callbacks, which are executed before or after {@link DynamicTransformer#transform}. Currently,
+ * just used to log errors after transformation.
+ */
+public class InspectitListener implements AgentBuilder.Listener {
+  private static final Logger log = LoggerFactory.getLogger(InspectitListener.class);
+
+  @Override
+  public void onError(
+      String typeName,
+      ClassLoader classLoader,
+      JavaModule module,
+      boolean loaded,
+      Throwable throwable) {
+    log.error("Dynamic transformation failed for type {} : {}", typeName, throwable.getMessage());
+  }
+
+  @Override
+  public void onDiscovery(
+      String typeName, ClassLoader classLoader, JavaModule module, boolean loaded) {}
+
+  @Override
+  public void onTransformation(
+      TypeDescription typeDescription,
+      ClassLoader classLoader,
+      JavaModule module,
+      boolean loaded,
+      DynamicType dynamicType) {}
+
+  @Override
+  public void onIgnored(
+      TypeDescription typeDescription,
+      ClassLoader classLoader,
+      JavaModule module,
+      boolean loaded) {}
+
+  @Override
+  public void onComplete(
+      String typeName, ClassLoader classLoader, JavaModule module, boolean loaded) {}
+}

src/main/java/rocks/inspectit/gepard/agent/transformation/TransformationManager.java

@@ -31,7 +31,9 @@ public static TransformationManager create(InstrumentationState instrumentationS
    */
   public AgentBuilder modify(AgentBuilder agentBuilder) {
     DynamicTransformer transformer = new DynamicTransformer(instrumentationState);
+    InspectitListener listener = new InspectitListener();
+
     // In the future, we might add a white- or black-list for types
-    return agentBuilder.type(any()).transform(transformer);
+    return agentBuilder.type(any()).transform(transformer).with(listener);
   }
 }