org.apache.brooklyn.util.javalang.AggregateClassLoader Maven / Gradle / Ivy
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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.brooklyn.util.javalang;
import java.io.IOException;
import java.net.URL;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import java.util.concurrent.CopyOnWriteArrayList;
import com.google.common.collect.Sets;
/** looks for classes and resources in the classloaders added here
*
* similar to XStream's CompositeClassLoader, but also supporting resources,
* exposing more info, a few conveniences, and a nice toString */
public class AggregateClassLoader extends ClassLoader {
// thread safe -- and all access in this class is also synchronized,
// so that reset is guaranteed not to interfere with an add(0, cl)
private final CopyOnWriteArrayList classLoaders = new CopyOnWriteArrayList();
private AggregateClassLoader() {
//Don't pass load requests to the app classloader,
//always relay to the classLoaders list.
super(null);
}
/** creates default instance, with classloaders of Object and AggregateClassLoader */
public static AggregateClassLoader newInstanceWithDefaultLoaders() {
AggregateClassLoader cl = new AggregateClassLoader();
cl.addFirst(AggregateClassLoader.class.getClassLoader()); // whichever classloader loaded this jar.
cl.addFirst(Object.class.getClassLoader()); // bootstrap loader.
return cl;
}
/** creates default instance, with no classloaders (assuming this instance will itself be nested,
* or defaults will be added by caller) */
public static AggregateClassLoader newInstanceWithNoLoaders() {
return new AggregateClassLoader();
}
/** Add a loader to the first position in the search path. */
public void addFirst(ClassLoader classLoader) {
if (classLoader != null) {
synchronized (classLoaders) {
classLoaders.add(0, classLoader);
}
}
}
/** Add a loader to the last position in the search path. */
public void addLast(ClassLoader classLoader) {
if (classLoader != null) {
synchronized (classLoaders) {
classLoaders.add(classLoader);
}
}
}
/** Add a loader to the specific position in the search path.
* (It is callers responsibility to ensure that position is valid.) */
public void add(int index, ClassLoader classLoader) {
if (classLoader != null) {
synchronized (classLoaders) {
classLoaders.add(index, classLoader);
}
}
}
/** Resets the classloader shown here to be the given set */
public void reset(Collection newClassLoaders) {
synchronized (classLoaders) {
// synchronize:
// * to prevent concurrent invocations
// * so add(0, cl) doesn't interfere
// * and for good measure we add before removing so that iterator always contains everything
// although since iterator access is synchronized that shouldn't be necessary
int count = classLoaders.size();
classLoaders.addAll(newClassLoaders);
for (int i=0; i getList() {
return classLoaders;
}
public Iterator iterator() {
synchronized (classLoaders) {
// CopyOnWriteList iterator is immutable view of snapshot
return classLoaders.iterator();
}
}
@Override
protected Class findClass(String name) throws ClassNotFoundException {
for (ClassLoader classLoader: classLoaders) {
try {
return classLoader.loadClass(name);
} catch (ClassNotFoundException notFound) {
/* ignore (nice if there were a better way than throwing... */
}
}
// last resort. see comment in XStream CompositeClassLoader
ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
if (contextClassLoader != null)
return contextClassLoader.loadClass(name);
throw new ClassNotFoundException(name);
}
@Override
public String toString() {
return "AggregateClassLoader"+classLoaders;
}
@Override
public URL getResource(String name) {
URL result = null;
Iterator cli = iterator();
while (cli.hasNext()) {
ClassLoader classLoader=cli.next();
result = classLoader.getResource(name);
if (result!=null) return result;
}
// last resort. see comment in XStream CompositeClassLoader
ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
if (contextClassLoader != null)
return contextClassLoader.getResource(name);
return null;
}
@Override
public Enumeration getResources(String name) throws IOException {
Set resources = Sets.newLinkedHashSet();
Iterator cli = iterator();
while (cli.hasNext()) {
ClassLoader classLoader=cli.next();
resources.addAll(Collections.list(classLoader.getResources(name)));
}
return Collections.enumeration(resources);
}
// TODO lesser used items, such as getPackage, findLibrary
}