org.glassfish.internal.api.DelegatingClassLoader Maven / Gradle / Ivy
/*
* Copyright (c) 2024 Contributors to the Eclipse Foundation.
* Copyright (c) 2007, 2018 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v. 2.0, which is available at
* http://www.eclipse.org/legal/epl-2.0.
*
* This Source Code may also be made available under the following Secondary
* Licenses when the conditions for such availability set forth in the
* Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
* version 2 with the GNU Classpath Exception, which is available at
* https://www.gnu.org/software/classpath/license.html.
*
* SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
*/
package org.glassfish.internal.api;
import com.sun.enterprise.module.common_impl.CompositeEnumeration;
import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;
import java.util.Objects;
import java.util.concurrent.CopyOnWriteArrayList;
import static java.util.Collections.unmodifiableList;
/**
* This class loader has a list of class loaders called as delegates
* that it uses to find classes.
*
* All those delegates must have the same parent as this class loader in order to
* have a consistent class space. By consistent class space, we mean a class space
* where no two loaded class have same name. An inconsistent class space can lead
* to {@link ClassCastException}.
*
* This class loader does not define any class, classes are always loaded either by
* its parent or by one of the delegates.
*
* @author [email protected]
*/
public class DelegatingClassLoader extends ClassLoader {
/**
* This interface is an optimization.
*
* The {@code findClass} method of {@link ClassLoader} is usually a protected method.
* Calling {@code loadClass} on a {@link ClassLoader} is expensive, as it searches
* the delegation hierarchy before searching in its private space.
*/
public interface ClassFinder {
/**
* Returns the paren class loader.
*
* The parent class loader used to check delegation hierarchy.
*
* @return the parent classloader
* @see ClassLoader#getParent()
*/
ClassLoader getParent();
/**
* Finds the class with the specified binary name.
*
* @param name the binary name of the class
* @return the resulting {@link Class} object
* @throws ClassNotFoundException if class could not be found
* @see ClassLoader#findClass(String)
*/
Class findClass(String name) throws ClassNotFoundException;
/**
* Returns the loaded class with the given binary name.
*
* @param name the binary name of the class
* @return the {@link Class} object, or {@code null} if the class has not been loaded
* @see ClassLoader#findLoadedClass(String)
*/
Class findExistingClass(String name);
/**
* Finds the resource with the given name.
*
* @param name the resource name
* @return a URL object for reading the resource, or {@code null} if the resource
* could not be found
* @see ClassLoader#findResource(String)
*/
URL findResource(String name);
/**
* Returns an enumeration of URL objects representing all resources with the given name.
*
* @param name the resource name
* @return an enumeration of URL objects for the resources
* @throws IOException if an I/O error occurs
* @see ClassLoader#findResources(String)
*/
Enumeration findResources(String name) throws IOException;
}
private final CopyOnWriteArrayList delegates = new CopyOnWriteArrayList<>();
/**
* Name of this class loader.
*
* Used mostly for reporting purpose.
*
* No guarantee about its uniqueness.
*/
private volatile String name;
/**
* Creates new delegating class loader.
*
* @throws IllegalArgumentException when the delegate does not have same parent
* as this class loader
*/
public DelegatingClassLoader(ClassLoader parent, List delegates) {
super(parent);
for (ClassFinder classFinder : delegates) {
checkDelegate(classFinder);
}
this.delegates.addAll(delegates);
}
public DelegatingClassLoader(ClassLoader parent) {
super(parent);
}
/**
* Adds a class finder to list of delegates.
*
* To have a consistent class space (by consistent class space, we mean a class space
* where there does not exist two class with same name), this method does not allow
* a delegate to be added that has a different parent.
*
* @param classFinder class finder to add to the list of delegates
* @return {@code true} if the delegate is added, {@code false} otherwise
* @throws IllegalArgumentException when the delegate does not have same parent
* as this class loader
*/
public boolean addDelegate(ClassFinder classFinder) {
checkDelegate(classFinder);
return delegates.addIfAbsent(classFinder);
}
/**
* Checks delegation hierarchy.
*
* @param classFinder class finder to check
* @throws IllegalArgumentException when the delegate does not have same parent
* as this class loader
*/
private void checkDelegate(ClassFinder classFinder) {
final ClassLoader delegateParent = classFinder.getParent();
final ClassLoader parent = getParent();
if (!Objects.equals(delegateParent, parent)) {
throw new IllegalArgumentException("Delegation hierarchy mismatch");
}
}
/**
* Removes a class finder from list of delegates.
*
* @param classFinder class finder to remove from the list of delegates
* @return {@code true} if the delegate was removed, {@code false} otherwise
*/
public boolean removeDelegate(ClassFinder classFinder) {
return delegates.remove(classFinder);
}
@Override
public Class findClass(String name) throws ClassNotFoundException {
for (ClassFinder classFinder : delegates) {
try {
Class c;
synchronized (classFinder) {
c = classFinder.findExistingClass(name);
if (c == null) {
c = classFinder.findClass(name);
}
}
return c;
} catch (ClassNotFoundException e) {
// Ignore, as we search next in list
}
}
throw new ClassNotFoundException(name);
}
@Override
protected URL findResource(String name) {
for (ClassFinder classFinder : delegates) {
URL resourceURL = classFinder.findResource(name);
if (resourceURL != null) {
return resourceURL;
}
}
return null;
}
@Override
protected Enumeration findResources(String name) throws IOException {
List> enumerators = new ArrayList<>();
for (ClassFinder classFinder : delegates) {
Enumeration enumerator = classFinder.findResources(name);
enumerators.add(enumerator);
}
return new CompositeEnumeration(enumerators);
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public List getDelegates() {
return unmodifiableList(delegates);
}
@Override
public String toString() {
if (name != null) {
return name;
} else {
return super.toString();
}
}
}