Spring Framework example source code file (ShadowingClassLoader.java)

This example Spring Framework source code file (ShadowingClassLoader.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Spring Framework tags/keywords

class, class, classloader, classnotfoundexception, classnotfoundexception, default_excluded_packages, enclosing, illegalstateexception, inputstream, io, ioexception, net, network, shadowingclassloader, shadowingclassloader, string, string, util

The Spring Framework ShadowingClassLoader.java source code

/*
 * 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.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.Enumeration;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

import org.springframework.core.DecoratingClassLoader;
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
 * @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 */
	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.",
					"org.apache.xerces.", "org.apache.commons.logging."};


	private final ClassLoader enclosingClassLoader;

	private final List<ClassFileTransformer> classFileTransformers = new LinkedList();

	private final Map<String, Class> classCache = new HashMap();


	/**
	 * Create a new ShadowingClassLoader, decorating the given ClassLoader.
	 * @param enclosingClassLoader the ClassLoader to decorate
	 */
	public ShadowingClassLoader(ClassLoader enclosingClassLoader) {
		Assert.notNull(enclosingClassLoader, "Enclosing ClassLoader must not be null");
		this.enclosingClassLoader = enclosingClassLoader;
		for (int i = 0; i < DEFAULT_EXCLUDED_PACKAGES.length; i++) {
			excludePackage(DEFAULT_EXCLUDED_PACKAGES[i]);
		}
	}


	/**
	 * 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);
	}


	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.
	 * @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) && !isClassNameExcludedFromShadowing(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);
	}

	/**
	 * Subclasses can override this method to specify whether or not a
	 * particular class should be excluded from shadowing.
	 * @param className the class name to test
	 * @return whether the specified class is excluded
	 * @deprecated in favor of {@link #isEligibleForShadowing}
	 */
	protected boolean isClassNameExcludedFromShadowing(String className) {
		return false;
	}


	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);
		}
	}


	public URL getResource(String name) {
		return this.enclosingClassLoader.getResource(name);
	}

	public InputStream getResourceAsStream(String name) {
		return this.enclosingClassLoader.getResourceAsStream(name);
	}

	public Enumeration<URL> getResources(String name) throws IOException {
		return this.enclosingClassLoader.getResources(name);
	}

}