001/*
002 * Copyright 2002-2018 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.instrument.classloading;
018
019import java.lang.instrument.ClassFileTransformer;
020import java.lang.reflect.Method;
021
022import org.apache.commons.logging.Log;
023import org.apache.commons.logging.LogFactory;
024
025import org.springframework.core.DecoratingClassLoader;
026import org.springframework.core.OverridingClassLoader;
027import org.springframework.lang.Nullable;
028import org.springframework.util.Assert;
029import org.springframework.util.ClassUtils;
030import org.springframework.util.ReflectionUtils;
031
032/**
033 * {@link LoadTimeWeaver} which uses reflection to delegate to an underlying ClassLoader
034 * with well-known transformation hooks. The underlying ClassLoader is expected to
035 * support the following weaving methods (as defined in the {@link LoadTimeWeaver}
036 * interface):
037 * <ul>
038 * <li>{@code public void addTransformer(java.lang.instrument.ClassFileTransformer)}:
039 * for registering the given ClassFileTransformer on this ClassLoader
040 * <li>{@code public ClassLoader getThrowawayClassLoader()}:
041 * for obtaining a throwaway class loader for this ClassLoader (optional;
042 * ReflectiveLoadTimeWeaver will fall back to a SimpleThrowawayClassLoader if
043 * that method isn't available)
044 * </ul>
045 *
046 * <p>Please note that the above methods <i>must</i> reside in a class that is
047 * publicly accessible, although the class itself does not have to be visible
048 * to the application's class loader.
049 *
050 * <p>The reflective nature of this LoadTimeWeaver is particularly useful when the
051 * underlying ClassLoader implementation is loaded in a different class loader itself
052 * (such as the application server's class loader which is not visible to the
053 * web application). There is no direct API dependency between this LoadTimeWeaver
054 * adapter and the underlying ClassLoader, just a 'loose' method contract.
055 *
056 * <p>This is the LoadTimeWeaver to use e.g. with the Resin application server
057 * version 3.1+.
058 *
059 * @author Costin Leau
060 * @author Juergen Hoeller
061 * @since 2.0
062 * @see #addTransformer(java.lang.instrument.ClassFileTransformer)
063 * @see #getThrowawayClassLoader()
064 * @see SimpleThrowawayClassLoader
065 */
066public class ReflectiveLoadTimeWeaver implements LoadTimeWeaver {
067
068        private static final String ADD_TRANSFORMER_METHOD_NAME = "addTransformer";
069
070        private static final String GET_THROWAWAY_CLASS_LOADER_METHOD_NAME = "getThrowawayClassLoader";
071
072        private static final Log logger = LogFactory.getLog(ReflectiveLoadTimeWeaver.class);
073
074
075        private final ClassLoader classLoader;
076
077        private final Method addTransformerMethod;
078
079        @Nullable
080        private final Method getThrowawayClassLoaderMethod;
081
082
083        /**
084         * Create a new ReflectiveLoadTimeWeaver for the current context class
085         * loader, <i>which needs to support the required weaving methods</i>.
086         */
087        public ReflectiveLoadTimeWeaver() {
088                this(ClassUtils.getDefaultClassLoader());
089        }
090
091        /**
092         * Create a new SimpleLoadTimeWeaver for the given class loader.
093         * @param classLoader the {@code ClassLoader} to delegate to for
094         * weaving (<i>must</i> support the required weaving methods).
095         * @throws IllegalStateException if the supplied {@code ClassLoader}
096         * does not support the required weaving methods
097         */
098        public ReflectiveLoadTimeWeaver(@Nullable ClassLoader classLoader) {
099                Assert.notNull(classLoader, "ClassLoader must not be null");
100                this.classLoader = classLoader;
101
102                Method addTransformerMethod = ClassUtils.getMethodIfAvailable(
103                                this.classLoader.getClass(), ADD_TRANSFORMER_METHOD_NAME, ClassFileTransformer.class);
104                if (addTransformerMethod == null) {
105                        throw new IllegalStateException(
106                                        "ClassLoader [" + classLoader.getClass().getName() + "] does NOT provide an " +
107                                        "'addTransformer(ClassFileTransformer)' method.");
108                }
109                this.addTransformerMethod = addTransformerMethod;
110
111                Method getThrowawayClassLoaderMethod = ClassUtils.getMethodIfAvailable(
112                                this.classLoader.getClass(), GET_THROWAWAY_CLASS_LOADER_METHOD_NAME);
113                // getThrowawayClassLoader method is optional
114                if (getThrowawayClassLoaderMethod == null) {
115                        if (logger.isDebugEnabled()) {
116                                logger.debug("The ClassLoader [" + classLoader.getClass().getName() + "] does NOT provide a " +
117                                                "'getThrowawayClassLoader()' method; SimpleThrowawayClassLoader will be used instead.");
118                        }
119                }
120                this.getThrowawayClassLoaderMethod = getThrowawayClassLoaderMethod;
121        }
122
123
124        @Override
125        public void addTransformer(ClassFileTransformer transformer) {
126                Assert.notNull(transformer, "Transformer must not be null");
127                ReflectionUtils.invokeMethod(this.addTransformerMethod, this.classLoader, transformer);
128        }
129
130        @Override
131        public ClassLoader getInstrumentableClassLoader() {
132                return this.classLoader;
133        }
134
135        @Override
136        public ClassLoader getThrowawayClassLoader() {
137                if (this.getThrowawayClassLoaderMethod != null) {
138                        ClassLoader target = (ClassLoader)
139                                        ReflectionUtils.invokeMethod(this.getThrowawayClassLoaderMethod, this.classLoader);
140                        return (target instanceof DecoratingClassLoader ? target :
141                                        new OverridingClassLoader(this.classLoader, target));
142                }
143                else {
144                        return new SimpleThrowawayClassLoader(this.classLoader);
145                }
146        }
147
148}