org.apache.catalina.webresources.TomcatURLStreamHandlerFactory Maven / Gradle / Ivy
/*
* 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.catalina.webresources;
import java.net.URL;
import java.net.URLStreamHandler;
import java.net.URLStreamHandlerFactory;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;
import org.apache.catalina.webresources.war.Handler;
public class TomcatURLStreamHandlerFactory implements URLStreamHandlerFactory {
private static final String WAR_PROTOCOL = "war";
private static final String CLASSPATH_PROTOCOL = "classpath";
// Singleton instance
private static volatile TomcatURLStreamHandlerFactory instance = null;
/**
* Obtain a reference to the singleton instance. It is recommended that callers check the value of
* {@link #isRegistered()} before using the returned instance.
*
* @return A reference to the singleton instance
*/
public static TomcatURLStreamHandlerFactory getInstance() {
getInstanceInternal(true);
return instance;
}
private static TomcatURLStreamHandlerFactory getInstanceInternal(boolean register) {
// Double checked locking. OK because instance is volatile.
if (instance == null) {
synchronized (TomcatURLStreamHandlerFactory.class) {
if (instance == null) {
instance = new TomcatURLStreamHandlerFactory(register);
}
}
}
return instance;
}
private final boolean registered;
// List of factories for application defined stream handler factories.
private final List userFactories = new CopyOnWriteArrayList<>();
/**
* Register this factory with the JVM. May be called more than once. The implementation ensures that registration
* only occurs once.
*
* @return true if the factory is already registered with the JVM or was successfully registered as a
* result of this call. false if the factory was disabled prior to this call.
*/
public static boolean register() {
return getInstanceInternal(true).isRegistered();
}
/**
* Prevent this this factory from registering with the JVM. May be called more than once.
*
* @return true if the factory is already disabled or was successfully disabled as a result of this
* call. false if the factory was already registered prior to this call.
*/
public static boolean disable() {
return !getInstanceInternal(false).isRegistered();
}
/**
* Release references to any user provided factories that have been loaded using the provided class loader. Called
* during web application stop to prevent memory leaks.
*
* @param classLoader The class loader to release
*/
public static void release(ClassLoader classLoader) {
if (instance == null) {
return;
}
List factories = instance.userFactories;
for (URLStreamHandlerFactory factory : factories) {
ClassLoader factoryLoader = factory.getClass().getClassLoader();
while (factoryLoader != null) {
if (classLoader.equals(factoryLoader)) {
// Implementation note: userFactories is a
// CopyOnWriteArrayList, so items are removed with
// List.remove() instead of usual Iterator.remove()
factories.remove(factory);
break;
}
factoryLoader = factoryLoader.getParent();
}
}
}
private TomcatURLStreamHandlerFactory(boolean register) {
// Hide default constructor
// Singleton pattern to ensure there is only one instance of this
// factory
this.registered = register;
if (register) {
URL.setURLStreamHandlerFactory(this);
}
}
public boolean isRegistered() {
return registered;
}
/**
* Since the JVM only allows a single call to {@link URL#setURLStreamHandlerFactory(URLStreamHandlerFactory)} and
* Tomcat needs to register a handler, provide a mechanism to allow applications to register their own handlers.
*
* @param factory The user provided factory to add to the factories Tomcat has already registered
*/
public void addUserFactory(URLStreamHandlerFactory factory) {
userFactories.add(factory);
}
@Override
public URLStreamHandler createURLStreamHandler(String protocol) {
// Tomcat's handler always takes priority so applications can't override
// it.
if (WAR_PROTOCOL.equals(protocol)) {
return new Handler();
} else if (CLASSPATH_PROTOCOL.equals(protocol)) {
return new ClasspathURLStreamHandler();
}
// Application handlers
for (URLStreamHandlerFactory factory : userFactories) {
URLStreamHandler handler = factory.createURLStreamHandler(protocol);
if (handler != null) {
return handler;
}
}
// Unknown protocol
return null;
}
}