Remove JDK 8 compatibility code from OAL V2

OAP server requires JDK 11+, so JDK 8 compatibility code is unnecessary.

- Remove SystemUtils.isJavaVersionAtMost checks in OALClassGeneratorV2
- Remove unused currentClassLoader field and setter
- Update OALEngineV2 and tests to remove setCurrentClassLoader calls
- Remove JavaVersion and SystemUtils imports

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: wu-sheng

oap-server/oal-rt/src/main/java/org/apache/skywalking/oal/v2/OALEngineV2.java

@@ -92,7 +92,6 @@ public void start(ClassLoader currentClassLoader) throws ModuleStartException, O
 
         // Prepare temp folder for generated classes
         classGeneratorV2.prepareRTTempFolder();
-        classGeneratorV2.setCurrentClassLoader(currentClassLoader);
 
         // Load OAL script, parse, and generate classes with proper resource management
         try (Reader reader = ResourceUtils.read(oalDefine.getConfigFile())) {

oap-server/oal-rt/src/main/java/org/apache/skywalking/oal/v2/generator/OALClassGeneratorV2.java

@@ -47,8 +47,6 @@
 import javassist.bytecode.annotation.StringMemberValue;
 import lombok.extern.slf4j.Slf4j;
 import org.apache.commons.io.FileUtils;
-import org.apache.commons.lang3.JavaVersion;
-import org.apache.commons.lang3.SystemUtils;
 import org.apache.skywalking.oap.server.core.WorkPath;
 import org.apache.skywalking.oap.server.core.analysis.DisableRegister;
 import org.apache.skywalking.oap.server.core.analysis.SourceDispatcher;
@@ -100,7 +98,6 @@ public class OALClassGeneratorV2 {
     private final ClassPool classPool;
     private final OALDefine oalDefine;
     private Configuration configuration;
-    private ClassLoader currentClassLoader;
     private StorageBuilderFactory storageBuilderFactory;
     private static String GENERATED_FILE_PATH;
 
@@ -282,11 +279,7 @@ private Class generateMetricsClass(CodeGenModel model) throws OALCompileExceptio
 
         Class targetClass;
         try {
-            if (SystemUtils.isJavaVersionAtMost(JavaVersion.JAVA_1_8)) {
-                targetClass = metricsClass.toClass(currentClassLoader, null);
-            } else {
-                targetClass = metricsClass.toClass(MetricClassPackageHolder.class);
-            }
+            targetClass = metricsClass.toClass(MetricClassPackageHolder.class);
         } catch (CannotCompileException e) {
             log.error("Can't compile/load " + className + ".", e);
             throw new OALCompileException(e.getMessage(), e);
@@ -337,11 +330,7 @@ private void generateMetricsBuilderClass(CodeGenModel model) throws OALCompileEx
         }
 
         try {
-            if (SystemUtils.isJavaVersionAtMost(JavaVersion.JAVA_1_8)) {
-                metricsBuilderClass.toClass(currentClassLoader, null);
-            } else {
-                metricsBuilderClass.toClass(MetricBuilderClassPackageHolder.class);
-            }
+            metricsBuilderClass.toClass(MetricBuilderClassPackageHolder.class);
         } catch (CannotCompileException e) {
             log.error("Can't compile/load " + className + ".", e);
             throw new OALCompileException(e.getMessage(), e);
@@ -408,11 +397,7 @@ private Class generateDispatcherClass(String scopeName, DispatcherContextV2 disp
 
         Class targetClass;
         try {
-            if (SystemUtils.isJavaVersionAtMost(JavaVersion.JAVA_1_8)) {
-                targetClass = dispatcherClass.toClass(currentClassLoader, null);
-            } else {
-                targetClass = dispatcherClass.toClass(DispatcherClassPackageHolder.class);
-            }
+            targetClass = dispatcherClass.toClass(DispatcherClassPackageHolder.class);
         } catch (CannotCompileException e) {
             log.error("Can't compile/load " + className + ".", e);
             throw new OALCompileException(e.getMessage(), e);
@@ -488,10 +473,6 @@ private void writeGeneratedFile(CtClass ctClass, String type) throws OALCompileE
         }
     }
 
-    public void setCurrentClassLoader(ClassLoader currentClassLoader) {
-        this.currentClassLoader = currentClassLoader;
-    }
-
     public void setStorageBuilderFactory(StorageBuilderFactory storageBuilderFactory) {
         this.storageBuilderFactory = storageBuilderFactory;
     }

oap-server/oal-rt/src/test/java/org/apache/skywalking/oal/v2/generator/OALClassGeneratorV2Test.java

@@ -420,7 +420,6 @@ public void testInFilterOperatorGeneration() throws Exception {
     private OALClassGeneratorV2 createGenerator() {
         TestOALDefine oalDefine = new TestOALDefine();
         OALClassGeneratorV2 generator = new OALClassGeneratorV2(oalDefine);
-        generator.setCurrentClassLoader(OALClassGeneratorV2Test.class.getClassLoader());
         generator.setStorageBuilderFactory(new StorageBuilderFactory.Default());
         generator.prepareRTTempFolder();
         return generator;

oap-server/oal-rt/src/test/java/org/apache/skywalking/oal/v2/generator/RuntimeOALGenerationTest.java

@@ -278,7 +278,6 @@ public void testGenerateAllRuntimeOALScripts() throws Exception {
                 OALClassGeneratorV2 generator = new OALClassGeneratorV2(define, classPool);
                 generator.setOpenEngineDebug(true);
                 generator.setStorageBuilderFactory(new StorageBuilderFactory.Default());
-                generator.setCurrentClassLoader(this.getClass().getClassLoader());
 
                 // Generate classes
                 List<Class> metricsClasses = new ArrayList<>();