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.core;
018
019import java.io.IOException;
020import java.io.InputStream;
021
022import org.springframework.lang.Nullable;
023import org.springframework.util.FileCopyUtils;
024
025/**
026 * {@code ClassLoader} that does <i>not</i> always delegate to the parent loader
027 * as normal class loaders do. This enables, for example, instrumentation to be
028 * forced in the overriding ClassLoader, or a "throwaway" class loading behavior
029 * where selected application classes are temporarily loaded in the overriding
030 * {@code ClassLoader} for introspection purposes before eventually loading an
031 * instrumented version of the class in the given parent {@code ClassLoader}.
032 *
033 * @author Rod Johnson
034 * @author Juergen Hoeller
035 * @since 2.0.1
036 */
037public class OverridingClassLoader extends DecoratingClassLoader {
038
039        /** Packages that are excluded by default. */
040        public static final String[] DEFAULT_EXCLUDED_PACKAGES = new String[]
041                        {"java.", "javax.", "sun.", "oracle.", "javassist.", "org.aspectj.", "net.sf.cglib."};
042
043        private static final String CLASS_FILE_SUFFIX = ".class";
044
045        static {
046                ClassLoader.registerAsParallelCapable();
047        }
048
049
050        @Nullable
051        private final ClassLoader overrideDelegate;
052
053
054        /**
055         * Create a new OverridingClassLoader for the given ClassLoader.
056         * @param parent the ClassLoader to build an overriding ClassLoader for
057         */
058        public OverridingClassLoader(@Nullable ClassLoader parent) {
059                this(parent, null);
060        }
061
062        /**
063         * Create a new OverridingClassLoader for the given ClassLoader.
064         * @param parent the ClassLoader to build an overriding ClassLoader for
065         * @param overrideDelegate the ClassLoader to delegate to for overriding
066         * @since 4.3
067         */
068        public OverridingClassLoader(@Nullable ClassLoader parent, @Nullable ClassLoader overrideDelegate) {
069                super(parent);
070                this.overrideDelegate = overrideDelegate;
071                for (String packageName : DEFAULT_EXCLUDED_PACKAGES) {
072                        excludePackage(packageName);
073                }
074        }
075
076
077        @Override
078        public Class<?> loadClass(String name) throws ClassNotFoundException {
079                if (this.overrideDelegate != null && isEligibleForOverriding(name)) {
080                        return this.overrideDelegate.loadClass(name);
081                }
082                return super.loadClass(name);
083        }
084
085        @Override
086        protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
087                if (isEligibleForOverriding(name)) {
088                        Class<?> result = loadClassForOverriding(name);
089                        if (result != null) {
090                                if (resolve) {
091                                        resolveClass(result);
092                                }
093                                return result;
094                        }
095                }
096                return super.loadClass(name, resolve);
097        }
098
099        /**
100         * Determine whether the specified class is eligible for overriding
101         * by this class loader.
102         * @param className the class name to check
103         * @return whether the specified class is eligible
104         * @see #isExcluded
105         */
106        protected boolean isEligibleForOverriding(String className) {
107                return !isExcluded(className);
108        }
109
110        /**
111         * Load the specified class for overriding purposes in this ClassLoader.
112         * <p>The default implementation delegates to {@link #findLoadedClass},
113         * {@link #loadBytesForClass} and {@link #defineClass}.
114         * @param name the name of the class
115         * @return the Class object, or {@code null} if no class defined for that name
116         * @throws ClassNotFoundException if the class for the given name couldn't be loaded
117         */
118        @Nullable
119        protected Class<?> loadClassForOverriding(String name) throws ClassNotFoundException {
120                Class<?> result = findLoadedClass(name);
121                if (result == null) {
122                        byte[] bytes = loadBytesForClass(name);
123                        if (bytes != null) {
124                                result = defineClass(name, bytes, 0, bytes.length);
125                        }
126                }
127                return result;
128        }
129
130        /**
131         * Load the defining bytes for the given class,
132         * to be turned into a Class object through a {@link #defineClass} call.
133         * <p>The default implementation delegates to {@link #openStreamForClass}
134         * and {@link #transformIfNecessary}.
135         * @param name the name of the class
136         * @return the byte content (with transformers already applied),
137         * or {@code null} if no class defined for that name
138         * @throws ClassNotFoundException if the class for the given name couldn't be loaded
139         */
140        @Nullable
141        protected byte[] loadBytesForClass(String name) throws ClassNotFoundException {
142                InputStream is = openStreamForClass(name);
143                if (is == null) {
144                        return null;
145                }
146                try {
147                        // Load the raw bytes.
148                        byte[] bytes = FileCopyUtils.copyToByteArray(is);
149                        // Transform if necessary and use the potentially transformed bytes.
150                        return transformIfNecessary(name, bytes);
151                }
152                catch (IOException ex) {
153                        throw new ClassNotFoundException("Cannot load resource for class [" + name + "]", ex);
154                }
155        }
156
157        /**
158         * Open an InputStream for the specified class.
159         * <p>The default implementation loads a standard class file through
160         * the parent ClassLoader's {@code getResourceAsStream} method.
161         * @param name the name of the class
162         * @return the InputStream containing the byte code for the specified class
163         */
164        @Nullable
165        protected InputStream openStreamForClass(String name) {
166                String internalName = name.replace('.', '/') + CLASS_FILE_SUFFIX;
167                return getParent().getResourceAsStream(internalName);
168        }
169
170
171        /**
172         * Transformation hook to be implemented by subclasses.
173         * <p>The default implementation simply returns the given bytes as-is.
174         * @param name the fully-qualified name of the class being transformed
175         * @param bytes the raw bytes of the class
176         * @return the transformed bytes (never {@code null};
177         * same as the input bytes if the transformation produced no changes)
178         */
179        protected byte[] transformIfNecessary(String name, byte[] bytes) {
180                return bytes;
181        }
182
183}