Java tutorial
/* * Copyright 2002-2008 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.arsenal.framework.core.loader; 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.Enumeration; import java.util.HashMap; import java.util.HashSet; import java.util.LinkedList; import java.util.List; import java.util.Map; import java.util.Set; import org.arsenal.framework.util.Assert; import org.arsenal.framework.util.StringUtils; import org.arsenal.framework.util.XIOUtils; public class ShadowingClassLoader extends ClassLoader { private final Set<String> excludedPackages = new HashSet<String>(); private final Set<String> excludedClasses = new HashSet<String>(); private final Object exclusionMonitor = new Object(); /** Packages that are excluded by default */ public static final String[] DEFAULT_EXCLUDED_PACKAGES = new String[] { "java.", "javax.", "sun.", "oracle.", "com.sun.", "com.ibm.", "COM.ibm.", "org.w3c.", "org.xml.", "org.dom4j.", "org.eclipse", "org.aspectj.", "net.sf.cglib.", "org.apache.xerces.", "org.apache.commons.logging." }; private final ClassLoader parentClassLoader; private final List<ClassFileTransformer> classFileTransformers = new LinkedList<ClassFileTransformer>(); private final Map<String, Class> classCache = new HashMap<String, Class>(); /** * Create a new ShadowingClassLoader, decorating the given ClassLoader. * @param parentClassLoader the ClassLoader to decorate */ public ShadowingClassLoader(ClassLoader parentClassLoader) { Assert.notNull(parentClassLoader, "Enclosing ClassLoader must not be null"); this.parentClassLoader = parentClassLoader; for (String excludedPackage : DEFAULT_EXCLUDED_PACKAGES) { excludePackage(excludedPackage); } } /** * 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. * @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.parentClassLoader.loadClass(name); } } /** * 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. * @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.parentClassLoader.getResourceAsStream(internalName); if (is == null) { throw new ClassNotFoundException(name); } try { byte[] bytes = XIOUtils.toByteArray(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.parentClassLoader.getResource(name); } @Override public InputStream getResourceAsStream(String name) { return this.parentClassLoader.getResourceAsStream(name); } @Override public Enumeration<URL> getResources(String name) throws IOException { return this.parentClassLoader.getResources(name); } /** * Add a package name to exclude from decoration (e.g. overriding). * <p>Any class whose fully-qualified name starts with the name registered * here will be handled by the parent ClassLoader in the usual fashion. * @param packageName the package name to exclude */ public void excludePackage(String packageName) { Assert.notNull(packageName, "Package name must not be null"); synchronized (this.exclusionMonitor) { this.excludedPackages.add(packageName); } } /** * Add a class name to exclude from decoration (e.g. overriding). * <p>Any class name registered here will be handled by the parent * ClassLoader in the usual fashion. * @param className the class name to exclude */ public void excludeClass(String className) { Assert.notNull(className, "Class name must not be null"); synchronized (this.exclusionMonitor) { this.excludedClasses.add(className); } } /** * Determine whether the specified class is excluded from decoration * by this class loader. * <p>The default implementation checks against excluded packages and classes. * @param className the class name to check * @return whether the specified class is eligible * @see #excludePackage * @see #excludeClass */ protected boolean isExcluded(String className) { synchronized (this.exclusionMonitor) { if (this.excludedClasses.contains(className)) { return true; } for (String packageName : this.excludedPackages) { if (className.startsWith(packageName)) { return true; } } } return false; } public static void main(String[] args) { ClassLoader loader = ClassLoader.getSystemClassLoader(); ShadowingClassLoader shadowLoader = new ShadowingClassLoader(loader); boolean shadow = shadowLoader.isEligibleForShadowing("SegSyncJobTaskMain"); System.out.println(shadow); //shadowLoader.loadClass(name); } }