/*
* 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.cocoon.jnet;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.net.URL;
import java.net.URLStreamHandler;
import java.net.URLStreamHandlerFactory;
/**
* The installer is a general purpose class to install an own {@link URLStreamHandlerFactory} in any environment.
*/
public class URLStreamHandlerFactoryInstaller {
public static void setURLStreamHandlerFactory(URLStreamHandlerFactory factory) throws Exception {
try {
// if we can set the factory, its the first!
URL.setURLStreamHandlerFactory(new ParentableURLStreamHandlerFactory(factory, null));
} catch (Error err) {
ParentableURLStreamHandlerFactory currentFactory = getCurrentFactory();
setCurrentFactory(new ParentableURLStreamHandlerFactory(factory, currentFactory));
}
}
private static ParentableURLStreamHandlerFactory getCurrentFactory() throws Exception {
Field factoryField = getFactoryField();
URLStreamHandlerFactory currentFactory = (URLStreamHandlerFactory) factoryField.get(null);
if (currentFactory instanceof ParentableURLStreamHandlerFactory) {
return (ParentableURLStreamHandlerFactory) currentFactory;
}
return new ParentableURLStreamHandlerFactory(currentFactory, null);
}
private static Field getFactoryField() throws Exception {
// let's use reflection to get the field holding the factory
final Field[] fields = URL.class.getDeclaredFields();
for (int i = 0; i < fields.length; i++) {
Field current = fields[i];
if (Modifier.isStatic(current.getModifiers()) && current.getType().equals(URLStreamHandlerFactory.class)) {
current.setAccessible(true);
return current;
}
}
throw new Exception("Unable to detect static field in the URL class for the URLStreamHandlerFactory."
+ " Please report this error together with your exact environment to the Apache Excalibur project.");
}
private static void setCurrentFactory(ParentableURLStreamHandlerFactory parentableURLStreamHandlerFactory) throws Exception {
Field factoryField = getFactoryField();
factoryField.set(null, parentableURLStreamHandlerFactory);
}
private static class ParentableURLStreamHandlerFactory implements URLStreamHandlerFactory {
private final URLStreamHandlerFactory factory;
private final ParentableURLStreamHandlerFactory parent;
public ParentableURLStreamHandlerFactory(URLStreamHandlerFactory factory, ParentableURLStreamHandlerFactory parent) {
super();
this.parent = parent;
this.factory = factory;
}
public URLStreamHandler createURLStreamHandler(String protocol) {
URLStreamHandler handler = this.factory.createURLStreamHandler(protocol);
if (handler == null && this.parent != null) {
handler = this.parent.createURLStreamHandler(protocol);
}
return handler;
}
}
}