@Override
    public final byte[] transform(@Nullable final ClassLoader loader, @Nullable final String classFile, final Class<?> classBeingRedefined,
                                  final ProtectionDomain protectionDomain, @NonNull final byte[] classFileBuffer) {
        try {
            // Lambda has no class file, no need to transform, just return.
            if (classFile == null) return NO_TRANSFORM;

            final ClassInfo classInfo = new ClassInfo(classFile, classFileBuffer, loader);
            if (isClassUnderPackage(classInfo.getClassName(), "com.alibaba.ttl")) return NO_TRANSFORM;
            if (isClassUnderPackage(classInfo.getClassName(), "java.lang")) return NO_TRANSFORM;

            if (logClassTransform)
                logger.info("[TtlTransformer] transforming " + classInfo.getClassName()
                        + " from classloader " + classInfo.getClassLoader()
                        + " at location " + classInfo.getLocationUrl());

            extensionTransformletManager.collectExtensionTransformlet(classInfo);

            for (TtlTransformlet transformlet : transformletList) {
                transformlet.doTransform(classInfo);
                if (classInfo.isModified()) {
                    logger.info("[TtlTransformer] " + transformlet.getClass().getName() + " transformed " + classInfo.getClassName()
                            + " from classloader " + classInfo.getClassLoader()
                            + " at location " + classInfo.getLocationUrl());
                    return classInfo.getCtClass().toBytecode();
                }
            }

            final String transformlet = extensionTransformletManager.extensionTransformletDoTransform(classInfo);
            if (classInfo.isModified()) {
                logger.info("[TtlTransformer] " + transformlet + " transformed " + classInfo.getClassName()
                        + " from classloader " + classInfo.getClassLoader()
                        + " at location " + classInfo.getLocationUrl());
                return classInfo.getCtClass().toBytecode();
            }
        } catch (Throwable t) {
            String msg = "[TtlTransformer] fail to transform class " + classFile + ", cause: " + t.toString();
            logger.error(msg, t);
            throw new IllegalStateException(msg, t);
        }

        return NO_TRANSFORM;
    }
info about class loader: may be <code>null</code> if the bootstrap loader.
<p>
more info see {@link ClassFileTransformer#transform(java.lang.ClassLoader, java.lang.String, java.lang.Class, java.security.ProtectionDomain, byte[])}
ttl2-compatible/src/main/java/com/alibaba/ttl/threadpool/agent/TtlTransformer.java