/*
* Copyright © 2014 Cask Data, Inc.
*
* Licensed 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 co.cask.tigon.internal.io;
import co.cask.tigon.internal.asm.ClassDefinition;
import co.cask.tigon.internal.lang.Fields;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.common.reflect.TypeToken;
import java.lang.reflect.Method;
/**
* A {@link FieldAccessorFactory} that uses ASM to generate a specific {@link FieldAccessor} class
* for each field. The resulting {@link FieldAccessor} instance will be cached and reused.
*/
public final class ASMFieldAccessorFactory implements FieldAccessorFactory {
private final LoadingCache<FieldEntry, FieldAccessor> fieldAccessorCache;
public ASMFieldAccessorFactory() {
this.fieldAccessorCache = CacheBuilder.newBuilder().build(new FieldAccessorLoader());
}
@Override
public FieldAccessor getFieldAccessor(TypeToken<?> type, String fieldName) {
return fieldAccessorCache.getUnchecked(new FieldEntry(type, fieldName));
}
/**
* The {@link com.google.common.cache.CacheLoader} for generating instance of {@link FieldAccessor} instance.
*/
private static final class FieldAccessorLoader extends CacheLoader<FieldEntry, FieldAccessor> {
// See if are able to use the "defineClass" method in the ClassLoader of the field class.
private final Method defineClass;
FieldAccessorLoader() {
Method defineClass = null;
try {
defineClass = ClassLoader.class.getDeclaredMethod("defineClass", String.class,
byte[].class, int.class, int.class);
defineClass.setAccessible(true);
} catch (Exception e) {
// ok to ignore this exception, it will resort to the slow reflection way.
}
this.defineClass = defineClass;
}
@Override
public FieldAccessor load(FieldEntry key) throws Exception {
// See if are able to use the "defineClass" method in the ClassLoader of the field class.
Method defineClass = null;
try {
defineClass = ClassLoader.class.getDeclaredMethod("defineClass", String.class,
byte[].class, int.class, int.class);
defineClass.setAccessible(true);
} catch (Exception e) {
// ok to ignore this exception, it will resort to the slow reflection way.
}
// Generate the FieldAccessor class bytecode.
ClassDefinition classDef = new FieldAccessorGenerator()
.generate(key.getType(),
Fields.findField(key.getType(), key.getFieldName()),
defineClass == null);
return createAccessor(key.getType(), classDef);
}
private FieldAccessor createAccessor(TypeToken<?> type, ClassDefinition classDef) throws Exception {
// Must use the same classloader as the type.
ClassLoader classLoader = type.getRawType().getClassLoader();
String className = classDef.getClassName();
Method findLoadedClass = ClassLoader.class.getDeclaredMethod("findLoadedClass", String.class);
findLoadedClass.setAccessible(true);
Class<?> result = (Class<?>) findLoadedClass.invoke(classLoader, className);
if (result == null) {
// Try to define the class from the same classloader of the given type.
byte[] bytecode = classDef.getBytecode();
result = (Class<?>) defineClass.invoke(classLoader, className, bytecode, 0, bytecode.length);
}
return (FieldAccessor) result.getConstructor(TypeToken.class).newInstance(type);
}
}
}