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/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.apache.xbean.classloader;
import java.io.IOException;
import java.net.URL;
import java.net.URLStreamHandlerFactory;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.List;
/**
* A MultiParentClassLoader is a simple extension of the URLClassLoader that simply changes the single parent class
* loader model to support a list of parent class loaders. Each operation that accesses a parent, has been replaced with
* a operation that checks each parent in order. This getParent method of this class will always return null, which may
* be interperated by the calling code to mean that this class loader is a direct child of the system class loader.
*
* @author Dain Sundstrom
*/
public class MultiParentClassLoader extends NamedClassLoader {
private static final Enumeration EMPTY_ENUMERATION = Collections.enumeration(new ArrayList());
private final ClassLoader[] parents;
private final boolean inverseClassLoading;
private final String[] hiddenClasses;
private final String[] nonOverridableClasses;
private final String[] hiddenResources;
private final String[] nonOverridableResources;
/**
* Creates a named class loader with no parents.
* @param name the name of this class loader
* @param urls the urls from which this class loader will classes and resources
*/
public MultiParentClassLoader(String name, URL[] urls) {
this(name, urls, ClassLoader.getSystemClassLoader());
}
/**
* Creates a named class loader as a child of the specified parent.
* @param name the name of this class loader
* @param urls the urls from which this class loader will classes and resources
* @param parent the parent of this class loader
*/
public MultiParentClassLoader(String name, URL[] urls, ClassLoader parent) {
this(name, urls, new ClassLoader[] { parent });
}
/**
* Creates a named class loader as a child of the specified parent and using the specified URLStreamHandlerFactory
* for accessing the urls..
* @param name the name of this class loader
* @param urls the urls from which this class loader will classes and resources
* @param parent the parent of this class loader
* @param factory the URLStreamHandlerFactory used to access the urls
*/
public MultiParentClassLoader(String name, URL[] urls, ClassLoader parent, URLStreamHandlerFactory factory) {
this(name, urls, new ClassLoader[] { parent }, factory);
}
/**
* Creates a named class loader as a child of the specified parents.
* @param name the name of this class loader
* @param urls the urls from which this class loader will classes and resources
* @param parents the parents of this class loader
*/
public MultiParentClassLoader(String name, URL[] urls, ClassLoader[] parents) {
this(name, urls, parents, false, new String[0], new String[0]);
}
public MultiParentClassLoader(String name, URL[] urls, ClassLoader parent, boolean inverseClassLoading,
String[] hiddenClasses, String[] nonOverridableClasses) {
this(name, urls, new ClassLoader[] { parent }, inverseClassLoading, hiddenClasses, nonOverridableClasses);
}
/**
* Creates a named class loader as a child of the specified parents and using the specified URLStreamHandlerFactory
* for accessing the urls..
* @param name the name of this class loader
* @param urls the urls from which this class loader will classes and resources
* @param parents the parents of this class loader
* @param factory the URLStreamHandlerFactory used to access the urls
*/
public MultiParentClassLoader(String name, URL[] urls, ClassLoader[] parents, URLStreamHandlerFactory factory) {
super(name, urls, null, factory);
this.parents = copyParents(parents);
this.inverseClassLoading = false;
this.hiddenClasses = new String[0];
this.nonOverridableClasses = new String[0];
this.hiddenResources = new String[0];
this.nonOverridableResources = new String[0];
}
public MultiParentClassLoader(String name, URL[] urls, ClassLoader[] parents, boolean inverseClassLoading,
Collection hiddenClasses, Collection nonOverridableClasses) {
this(name, urls, parents, inverseClassLoading, hiddenClasses.toArray(new String[hiddenClasses.size()]),
nonOverridableClasses.toArray(new String[nonOverridableClasses.size()]));
}
public MultiParentClassLoader(String name, URL[] urls, ClassLoader[] parents, boolean inverseClassLoading,
String[] hiddenClasses, String[] nonOverridableClasses) {
super(name, urls);
this.parents = copyParents(parents);
this.inverseClassLoading = inverseClassLoading;
this.hiddenClasses = hiddenClasses;
this.nonOverridableClasses = nonOverridableClasses;
hiddenResources = toResources(hiddenClasses);
nonOverridableResources = toResources(nonOverridableClasses);
}
private static String[] toResources(String[] classes) {
String[] resources = new String[classes.length];
for (int i = 0; i < classes.length; i++) {
String className = classes[i];
resources[i] = className.replace('.', '/');
}
return resources;
}
private static ClassLoader[] copyParents(ClassLoader[] parents) {
ClassLoader[] newParentsArray = new ClassLoader[parents.length];
for (int i = 0; i < parents.length; i++) {
ClassLoader parent = parents[i];
if (parent == null) {
throw new NullPointerException("parent[" + i + "] is null");
}
newParentsArray[i] = parent;
}
return newParentsArray;
}
/**
* Gets the parents of this class loader.
* @return the parents of this class loader
*/
public ClassLoader[] getParents() {
return parents;
}
/**
* {@inheritDoc}
*/
protected synchronized Class loadClass(String name, boolean resolve) throws ClassNotFoundException {
// Check if class is in the loaded classes cache
Class cachedClass = findLoadedClass(name);
if (cachedClass != null) {
return resolveClass(cachedClass, resolve);
}
// if we are using inverse class loading, check local urls first
if (inverseClassLoading && !isDestroyed() && !isNonOverridableClass(name)) {
try {
Class clazz = findClass(name);
return resolveClass(clazz, resolve);
} catch (ClassNotFoundException ignored) {
}
}
// Check parent class loaders
if (!isHiddenClass(name)) {
for (int i = 0; i < parents.length; i++) {
ClassLoader parent = parents[i];
try {
Class clazz = parent.loadClass(name);
return resolveClass(clazz, resolve);
} catch (ClassNotFoundException ignored) {
// this parent didn't have the class; try the next one
}
}
}
// if we are not using inverse class loading, check local urls now
// don't worry about excluding non-overridable classes here... we
// have alredy checked he parent and the parent didn't have the
// class, so we can override now
if (!isDestroyed()) {
try {
Class clazz = findClass(name);
return resolveClass(clazz, resolve);
} catch (ClassNotFoundException ignored) {
}
}
throw new ClassNotFoundException(name + " in classloader " + getName());
}
private boolean isNonOverridableClass(String name) {
for (int i = 0; i < nonOverridableClasses.length; i++) {
if (name.startsWith(nonOverridableClasses[i])) {
return true;
}
}
return false;
}
private boolean isHiddenClass(String name) {
for (int i = 0; i < hiddenClasses.length; i++) {
if (name.startsWith(hiddenClasses[i])) {
return true;
}
}
return false;
}
private Class resolveClass(Class clazz, boolean resolve) {
if (resolve) {
resolveClass(clazz);
}
return clazz;
}
/**
* {@inheritDoc}
*/
public URL getResource(String name) {
if (isDestroyed()) {
return null;
}
// if we are using inverse class loading, check local urls first
if (inverseClassLoading && !isDestroyed() && !isNonOverridableResource(name)) {
URL url = findResource(name);
if (url != null) {
return url;
}
}
// Check parent class loaders
if (!isHiddenResource(name)) {
for (int i = 0; i < parents.length; i++) {
ClassLoader parent = parents[i];
URL url = parent.getResource(name);
if (url != null) {
return url;
}
}
}
// if we are not using inverse class loading, check local urls now
// don't worry about excluding non-overridable resources here... we
// have alredy checked he parent and the parent didn't have the
// resource, so we can override now
if (!isDestroyed()) {
// parents didn't have the resource; attempt to load it from my urls
return findResource(name);
}
return null;
}
/**
* {@inheritDoc}
*/
public Enumeration findResources(String name) throws IOException {
if (isDestroyed()) {
return EMPTY_ENUMERATION;
}
List resources = new ArrayList();
// if we are using inverse class loading, add the resources from local urls first
if (inverseClassLoading && !isDestroyed()) {
List myResources = Collections.list(super.findResources(name));
resources.addAll(myResources);
}
// Add parent resources
for (int i = 0; i < parents.length; i++) {
ClassLoader parent = parents[i];
List parentResources = Collections.list(parent.getResources(name));
resources.addAll(parentResources);
}
// if we are not using inverse class loading, add the resources from local urls now
if (!inverseClassLoading && !isDestroyed()) {
List myResources = Collections.list(super.findResources(name));
resources.addAll(myResources);
}
return Collections.enumeration(resources);
}
private boolean isNonOverridableResource(String name) {
for (int i = 0; i < nonOverridableResources.length; i++) {
if (name.startsWith(nonOverridableResources[i])) {
return true;
}
}
return false;
}
private boolean isHiddenResource(String name) {
for (int i = 0; i < hiddenResources.length; i++) {
if (name.startsWith(hiddenResources[i])) {
return true;
}
}
return false;
}
/**
* {@inheritDoc}
*/
public String toString() {
return "[" + getClass().getName() + ":" + " name=" + getName() + " urls=" + Arrays.asList(getURLs())
+ " parents=" + Arrays.asList(parents) + "]";
}
}
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