/*
 * Copyright 2002-2020 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.
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package org.springframework.instrument.classloading;

import java.io.IOException;
import java.io.InputStream;
import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.springframework.core.DecoratingClassLoader;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.FileCopyUtils;
import org.springframework.util.StringUtils;

ClassLoader decorator that shadows an enclosing ClassLoader, applying registered transformers to all affected classes.
Author:Rob Harrop, Juergen Hoeller, Costin Leau
See Also:
Since:2.0
/** * ClassLoader decorator that shadows an enclosing ClassLoader, * applying registered transformers to all affected classes. * * @author Rob Harrop * @author Juergen Hoeller * @author Costin Leau * @since 2.0 * @see #addTransformer * @see org.springframework.core.OverridingClassLoader */
public class ShadowingClassLoader extends DecoratingClassLoader {
Packages that are excluded by default.
/** Packages that are excluded by default. */
public static final String[] DEFAULT_EXCLUDED_PACKAGES = new String[] {"java.", "javax.", "jdk.", "sun.", "oracle.", "com.sun.", "com.ibm.", "COM.ibm.", "org.w3c.", "org.xml.", "org.dom4j.", "org.eclipse", "org.aspectj.", "net.sf.cglib", "org.springframework.cglib", "org.apache.xerces.", "org.apache.commons.logging."}; private final ClassLoader enclosingClassLoader; private final List<ClassFileTransformer> classFileTransformers = new ArrayList<>(1); private final Map<String, Class<?>> classCache = new HashMap<>();
Create a new ShadowingClassLoader, decorating the given ClassLoader, applying DEFAULT_EXCLUDED_PACKAGES.
Params:
  • enclosingClassLoader – the ClassLoader to decorate
See Also:
/** * Create a new ShadowingClassLoader, decorating the given ClassLoader, * applying {@link #DEFAULT_EXCLUDED_PACKAGES}. * @param enclosingClassLoader the ClassLoader to decorate * @see #ShadowingClassLoader(ClassLoader, boolean) */
public ShadowingClassLoader(ClassLoader enclosingClassLoader) { this(enclosingClassLoader, true); }
Create a new ShadowingClassLoader, decorating the given ClassLoader.
Params:
Since:4.3.8
/** * Create a new ShadowingClassLoader, decorating the given ClassLoader. * @param enclosingClassLoader the ClassLoader to decorate * @param defaultExcludes whether to apply {@link #DEFAULT_EXCLUDED_PACKAGES} * @since 4.3.8 */
public ShadowingClassLoader(ClassLoader enclosingClassLoader, boolean defaultExcludes) { Assert.notNull(enclosingClassLoader, "Enclosing ClassLoader must not be null"); this.enclosingClassLoader = enclosingClassLoader; if (defaultExcludes) { for (String excludedPackage : DEFAULT_EXCLUDED_PACKAGES) { excludePackage(excludedPackage); } } }
Add the given ClassFileTransformer to the list of transformers that this ClassLoader will apply.
Params:
  • transformer – the ClassFileTransformer
/** * Add the given ClassFileTransformer to the list of transformers that this * ClassLoader will apply. * @param transformer the ClassFileTransformer */
public void addTransformer(ClassFileTransformer transformer) { Assert.notNull(transformer, "Transformer must not be null"); this.classFileTransformers.add(transformer); }
Copy all ClassFileTransformers from the given ClassLoader to the list of transformers that this ClassLoader will apply.
Params:
  • other – the ClassLoader to copy from
/** * Copy all ClassFileTransformers from the given ClassLoader to the list of * transformers that this ClassLoader will apply. * @param other the ClassLoader to copy from */
public void copyTransformers(ShadowingClassLoader other) { Assert.notNull(other, "Other ClassLoader must not be null"); this.classFileTransformers.addAll(other.classFileTransformers); } @Override public Class<?> loadClass(String name) throws ClassNotFoundException { if (shouldShadow(name)) { Class<?> cls = this.classCache.get(name); if (cls != null) { return cls; } return doLoadClass(name); } else { return this.enclosingClassLoader.loadClass(name); } }
Determine whether the given class should be excluded from shadowing.
Params:
  • className – the name of the class
Returns:whether the specified class should be shadowed
/** * Determine whether the given class should be excluded from shadowing. * @param className the name of the class * @return whether the specified class should be shadowed */
private boolean shouldShadow(String className) { return (!className.equals(getClass().getName()) && !className.endsWith("ShadowingClassLoader") && isEligibleForShadowing(className)); }
Determine whether the specified class is eligible for shadowing by this class loader.
Params:
  • className – the class name to check
See Also:
Returns:whether the specified class is eligible
/** * Determine whether the specified class is eligible for shadowing * by this class loader. * @param className the class name to check * @return whether the specified class is eligible * @see #isExcluded */
protected boolean isEligibleForShadowing(String className) { return !isExcluded(className); } private Class<?> doLoadClass(String name) throws ClassNotFoundException { String internalName = StringUtils.replace(name, ".", "/") + ".class"; InputStream is = this.enclosingClassLoader.getResourceAsStream(internalName); if (is == null) { throw new ClassNotFoundException(name); } try { byte[] bytes = FileCopyUtils.copyToByteArray(is); bytes = applyTransformers(name, bytes); Class<?> cls = defineClass(name, bytes, 0, bytes.length); // Additional check for defining the package, if not defined yet. if (cls.getPackage() == null) { int packageSeparator = name.lastIndexOf('.'); if (packageSeparator != -1) { String packageName = name.substring(0, packageSeparator); definePackage(packageName, null, null, null, null, null, null, null); } } this.classCache.put(name, cls); return cls; } catch (IOException ex) { throw new ClassNotFoundException("Cannot load resource for class [" + name + "]", ex); } } private byte[] applyTransformers(String name, byte[] bytes) { String internalName = StringUtils.replace(name, ".", "/"); try { for (ClassFileTransformer transformer : this.classFileTransformers) { byte[] transformed = transformer.transform(this, internalName, null, null, bytes); bytes = (transformed != null ? transformed : bytes); } return bytes; } catch (IllegalClassFormatException ex) { throw new IllegalStateException(ex); } } @Override public URL getResource(String name) { return this.enclosingClassLoader.getResource(name); } @Override @Nullable public InputStream getResourceAsStream(String name) { return this.enclosingClassLoader.getResourceAsStream(name); } @Override public Enumeration<URL> getResources(String name) throws IOException { return this.enclosingClassLoader.getResources(name); } }