convert UnsafeTest to java

javaagent-tooling/javaagent-tooling-java9/build.gradle.kts

@@ -29,4 +29,12 @@ tasks {
       compilerArgs.add("-Xlint:none")
     }
   }
+  compileTestJava {
+    with(options) {
+      // Because this module targets Java 9, we trigger this compiler bug which was fixed but not
+      // backported to Java 9 compilation.
+      // https://bugs.openjdk.java.net/browse/JDK-8209058
+      compilerArgs.add("-Xlint:none")
+    }
+  }
 }

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

@@ -22,7 +22,8 @@ static void initialize(Instrumentation instrumentation, ClassLoader classLoader)
     initialize(instrumentation, classLoader, true);
   }
 
-  private static void initialize(
+  // visible for testing
+  static void initialize(
       Instrumentation instrumentation, ClassLoader classLoader, boolean testUnsafePresent) {
     Class<?> unsafeClass;
     try {

javaagent-tooling/javaagent-tooling-java9/src/test/java/io/opentelemetry/javaagent/tooling/UnsafeTest.java

@@ -0,0 +1,32 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.javaagent.tooling;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import io.opentelemetry.javaagent.bootstrap.AgentClassLoader;
+import java.io.File;
+import java.net.URL;
+import net.bytebuddy.agent.ByteBuddyAgent;
+import org.junit.jupiter.api.Test;
+
+class UnsafeTest {
+
+  @Test
+  void testGenerateSunMiscUnsafe() throws Exception {
+    ByteBuddyAgent.install();
+    URL testJarLocation =
+        AgentClassLoader.class.getProtectionDomain().getCodeSource().getLocation();
+
+    try (AgentClassLoader loader = new AgentClassLoader(new File(testJarLocation.toURI()))) {
+      UnsafeInitializer.initialize(ByteBuddyAgent.getInstrumentation(), loader, false);
+
+      Class<?> unsafeClass = loader.loadClass("sun.misc.Unsafe");
+
+      assertThat(unsafeClass.getClassLoader()).isEqualTo(loader);
+    }
+  }
+}