use module opener only when supported

Author: SylvainJuge

javaagent-tooling/javaagent-tooling-java9/src/main/java/io/opentelemetry/javaagent/tooling/ModuleOpener.java

@@ -17,6 +17,13 @@
 import java.util.Set;
 import java.util.logging.Logger;
 
+/**
+ * Module opener provides ability to open JPMS modules and allows instrumentation classloader to
+ * access module contents without requiring JVM arguments modification. <br>
+ * Usage of this class must be guarded with an {@code net.bytebuddy.utility.JavaModule#isSupported}
+ * check as it's compiled for Java 9+, otherwise an {@link UnsupportedClassVersionError} will be
+ * thrown for java 8.
+ */
 public class ModuleOpener {
 
   private static final Logger logger = Logger.getLogger(ModuleOpener.class.getName());

javaagent-tooling/src/main/java/io/opentelemetry/javaagent/tooling/instrumentation/indy/IndyModuleRegistry.java

@@ -14,6 +14,7 @@
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 import net.bytebuddy.agent.builder.AgentBuilder;
+import net.bytebuddy.utility.JavaModule;
 
 public class IndyModuleRegistry {
 
@@ -88,19 +89,22 @@ public static InstrumentationModuleClassLoader getInstrumentationClassLoader(
         throw new IllegalStateException("global instrumentation not available");
       }
 
-      experimentalModule
-          .jpmsModulesToOpen()
-          .forEach(
-              (className, packages) -> {
-                Class<?> type;
-                try {
-                  type = Class.forName(className, false, instrumentedClassLoader);
-                } catch (ClassNotFoundException e) {
-                  throw new IllegalStateException("missing witness class " + className, e);
-                }
-
-                ModuleOpener.open(instrumentation, type, loader, packages);
-              });
+      if (JavaModule.isSupported()) {
+        // module opener only usable for java 9+
+        experimentalModule
+            .jpmsModulesToOpen()
+            .forEach(
+                (className, packages) -> {
+                  Class<?> type;
+                  try {
+                    type = Class.forName(className, false, instrumentedClassLoader);
+                  } catch (ClassNotFoundException e) {
+                    throw new IllegalStateException("missing witness class " + className, e);
+                  }
+
+                  ModuleOpener.open(instrumentation, type, loader, packages);
+                });
+      }
     }
     return loader;
   }