如何在没有 Spring 的情况下启用休眠字节码增强

Question

I have a plain java project using Hibernate / JPA. No Spring. No J2EE. And i want to enable runtime bytecode enhancement. A custom class loader is already inside the project so i think i could use org.hibernate.bytecode.spi.InstrumentedClassLoader.InstrumentedClassLoader(ClassLoader, ClassTransformer). But how to get the needed ClassTransformer? Or am i on the wrong track?

Answer 1

works if a ClassFileTransformerAdapter is added as transformer in the premain of a javaagent. (see http://appcrawler.com/wordpress/2013/01/02/simple-byte-code-injection-example-with-javassist/ )

needs "-javaagent:enhancer.jar" as Vm Argument

public class EnhancerMain {
  public static void premain(String agentArguments, Instrumentation instrumentation) {
    System.out.println("install enhancer");
    instrumentation.addTransformer(new ClassFileTransformerAdapter(new EnhancingClassTransformerImpl(new DefaultEnhancementContext())));
  }
}

public class ClassFileTransformerAdapter implements ClassFileTransformer {

  private final ClassTransformer classTransformer;

  public ClassFileTransformerAdapter(ClassTransformer classTransformer) {
    Objects.requireNonNull(classTransformer);
    this.classTransformer = classTransformer;
  }

  public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) {
    if (className.startsWith("java/")) {
      return null;
    }
    if (className.startsWith("sun/")) {
      return null;
    }
    if (className.startsWith("com/sun/")) {
      return null;
    }
    if (className.startsWith("javax/")) {
      return null;
    }
    try {
      byte[] transformed = this.classTransformer.transform(loader, className, classBeingRedefined, protectionDomain, classfileBuffer);
      return transformed;
    } catch (IllegalClassFormatException e) {
      throw new IllegalStateException("Error enhancing class: " + className, e);
    }
  }
}

Manifest-Version: 1.0
Premain-Class: com.enhancer.EnhancerMain