org.springframework.instrument.classloading.ReflectiveLoadTimeWeaver Maven / Gradle / Ivy
/*
* Copyright 2002-2007 the original author or authors.
*
* 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 org.springframework.instrument.classloading;
import java.lang.instrument.ClassFileTransformer;
import java.lang.reflect.Method;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.ReflectionUtils;
/**
* LoadTimeWeaver which uses reflection to delegate to an underlying ClassLoader
* with well-known transformation hooks. The underlying ClassLoader is expected to
* support the following weaving methods (as defined in the {@link LoadTimeWeaver}
* interface):
*
* public void addTransformer(java.lang.instrument.ClassFileTransformer):
* for registering the given ClassFileTransformer on this ClassLoader
* public ClassLoader getThrowawayClassLoader():
* for obtaining a throwaway class loader for this ClassLoader (optional;
* ReflectiveLoadTimeWeaver will fall back to a SimpleThrowawayClassLoader if
* that method isn't available)
*
*
* Please note that the above methods must reside in a class that is
* publicly accessible, although the class itself does not have to be visible
* to the application's class loader.
*
*
The reflective nature of this LoadTimeWeaver is particularly useful when the
* underlying class loader implementation is loaded in a different class loader
* (such as the application server's class loader which is not visible to the
* web application). There is no direct API dependency between this LoadTimeWeaver
* adapter and the underlying ClassLoader, just a 'loose' method contract.
*
*
This is the LoadTimeWeaver to use in combination with Spring's
* {@link org.springframework.instrument.classloading.tomcat.TomcatInstrumentableClassLoader}.
*
* @author Costin Leau
* @author Juergen Hoeller
* @since 2.0
* @see #addTransformer(java.lang.instrument.ClassFileTransformer)
* @see #getThrowawayClassLoader()
* @see SimpleThrowawayClassLoader
* @see org.springframework.instrument.classloading.tomcat.TomcatInstrumentableClassLoader
*/
public class ReflectiveLoadTimeWeaver implements LoadTimeWeaver {
private static final String ADD_TRANSFORMER_METHOD_NAME = "addTransformer";
private static final String GET_THROWAWAY_CLASS_LOADER_METHOD_NAME = "getThrowawayClassLoader";
private static final Log logger = LogFactory.getLog(ReflectiveLoadTimeWeaver.class);
private final ClassLoader classLoader;
private final Method addTransformerMethod;
private final Method getThrowawayClassLoaderMethod;
/**
* Create a new ReflectiveLoadTimeWeaver for the current context class
* loader, which needs to support the required weaving methods.
*/
public ReflectiveLoadTimeWeaver() {
this(ClassUtils.getDefaultClassLoader());
}
/**
* Create a new SimpleLoadTimeWeaver for the given class loader.
* @param classLoader the ClassLoader to delegate to for
* weaving (must support the required weaving methods).
* @throws IllegalArgumentException if the supplied ClassLoader
* is null
* @throws IllegalStateException if the supplied ClassLoader
* does not support the required weaving methods
*/
public ReflectiveLoadTimeWeaver(ClassLoader classLoader) {
Assert.notNull(classLoader, "ClassLoader must not be null");
this.classLoader = classLoader;
this.addTransformerMethod = ClassUtils.getMethodIfAvailable(
this.classLoader.getClass(), ADD_TRANSFORMER_METHOD_NAME,
new Class [] {ClassFileTransformer.class});
if (this.addTransformerMethod == null) {
throw new IllegalStateException(
"ClassLoader [" + classLoader.getClass().getName() + "] does NOT provide an " +
"'addTransformer(ClassFileTransformer)' method.");
}
this.getThrowawayClassLoaderMethod = ClassUtils.getMethodIfAvailable(
this.classLoader.getClass(), GET_THROWAWAY_CLASS_LOADER_METHOD_NAME,
new Class[0]);
// getThrowawayClassLoader method is optional
if (this.getThrowawayClassLoaderMethod == null) {
if (logger.isInfoEnabled()) {
logger.info("The ClassLoader [" + classLoader.getClass().getName() + "] does NOT provide a " +
"'getThrowawayClassLoader()' method; SimpleThrowawayClassLoader will be used instead.");
}
}
}
public void addTransformer(ClassFileTransformer transformer) {
Assert.notNull(transformer, "Transformer must not be null");
ReflectionUtils.invokeMethod(this.addTransformerMethod, this.classLoader, new Object[] {transformer});
}
public ClassLoader getInstrumentableClassLoader() {
return this.classLoader;
}
public ClassLoader getThrowawayClassLoader() {
if (this.getThrowawayClassLoaderMethod != null) {
return (ClassLoader) ReflectionUtils.invokeMethod(this.getThrowawayClassLoaderMethod, this.classLoader,
new Object[0]);
}
else {
return new SimpleThrowawayClassLoader(this.classLoader);
}
}
}