/*****************************************************************
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
****************************************************************/
package org.apache.cayenne.enhancer;
import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.ClassWriter;
/**
* A ClassFileTransformer that delegates class enhancement to a chain of ASM transformers
* provided by the {@link EnhancerVisitorFactory}.
*
* @since 3.0
*/
public class Enhancer implements ClassFileTransformer {
protected Log logger;
protected EnhancerVisitorFactory visitorFactory;
public Enhancer(EnhancerVisitorFactory visitorFactory) {
logger = LogFactory.getLog(getClass());
this.visitorFactory = visitorFactory;
}
public byte[] transform(
ClassLoader loader,
String className,
Class<?> classBeingRedefined,
ProtectionDomain protectionDomain,
byte[] classfileBuffer) throws IllegalClassFormatException {
ClassReader reader = new ClassReader(classfileBuffer);
// optimization note: per ASM docs COMPUTE_FRAMES makes code generation 2x slower,
// so we may investigate manual computation options, although that's likely a
// pain.
ClassWriter writer = new ClassWriter(reader, ClassWriter.COMPUTE_FRAMES);
ClassVisitor visitor = visitorFactory.createVisitor(className, writer);
if (visitor == null) {
// per instrumentation docs, if no transformation occured, we must return null
return null;
}
logger.info("enhancing class " + className);
try {
reader.accept(visitor, 0);
}
catch (DoubleEnhanceException e) {
logger.info("class already enhanced, skipping: " + className);
return null;
}
return writer.toByteArray();
}
}