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/*
 * Copyright 2002-2018 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
 *
 *      https://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.core.DecoratingClassLoader;
import org.springframework.core.OverridingClassLoader;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.ReflectionUtils;

/**
 * {@link 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):
 * 
    *
  • {@code public void addTransformer(java.lang.instrument.ClassFileTransformer)}: * for registering the given ClassFileTransformer on this ClassLoader *
  • {@code 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 ClassLoader implementation is loaded in a different class loader itself * (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 e.g. with the Resin application server * version 3.1+. * * @author Costin Leau * @author Juergen Hoeller * @since 2.0 * @see #addTransformer(java.lang.instrument.ClassFileTransformer) * @see #getThrowawayClassLoader() * @see SimpleThrowawayClassLoader */ 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; @Nullable 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 {@code ClassLoader} to delegate to for * weaving (must support the required weaving methods). * @throws IllegalStateException if the supplied {@code ClassLoader} * does not support the required weaving methods */ public ReflectiveLoadTimeWeaver(@Nullable ClassLoader classLoader) { Assert.notNull(classLoader, "ClassLoader must not be null"); this.classLoader = classLoader; Method addTransformerMethod = ClassUtils.getMethodIfAvailable( this.classLoader.getClass(), ADD_TRANSFORMER_METHOD_NAME, ClassFileTransformer.class); if (addTransformerMethod == null) { throw new IllegalStateException( "ClassLoader [" + classLoader.getClass().getName() + "] does NOT provide an " + "'addTransformer(ClassFileTransformer)' method."); } this.addTransformerMethod = addTransformerMethod; Method getThrowawayClassLoaderMethod = ClassUtils.getMethodIfAvailable( this.classLoader.getClass(), GET_THROWAWAY_CLASS_LOADER_METHOD_NAME); // getThrowawayClassLoader method is optional if (getThrowawayClassLoaderMethod == null) { if (logger.isDebugEnabled()) { logger.debug("The ClassLoader [" + classLoader.getClass().getName() + "] does NOT provide a " + "'getThrowawayClassLoader()' method; SimpleThrowawayClassLoader will be used instead."); } } this.getThrowawayClassLoaderMethod = getThrowawayClassLoaderMethod; } @Override public void addTransformer(ClassFileTransformer transformer) { Assert.notNull(transformer, "Transformer must not be null"); ReflectionUtils.invokeMethod(this.addTransformerMethod, this.classLoader, transformer); } @Override public ClassLoader getInstrumentableClassLoader() { return this.classLoader; } @Override public ClassLoader getThrowawayClassLoader() { if (this.getThrowawayClassLoaderMethod != null) { ClassLoader target = (ClassLoader) ReflectionUtils.invokeMethod(this.getThrowawayClassLoaderMethod, this.classLoader); return (target instanceof DecoratingClassLoader ? target : new OverridingClassLoader(this.classLoader, target)); } else { return new SimpleThrowawayClassLoader(this.classLoader); } } }





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