/*

  * 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.commons.jnet;

 import java.lang.reflect.Field;

 import java.lang.reflect.Modifier;

 import java.net.URL;

 import java.net.URLStreamHandlerFactory;

 /**

  * The installer is a general purpose class to install an own

  * {@link URLStreamHandlerFactory} in any environment.

  *

  * TODO Uninstall

  */

 public class Installer {

     /**

      * Set the url stream handler factory.

      * @param factory

      * @throws Exception

      */

     public static void setURLStreamHandlerFactory(URLStreamHandlerFactory factory)

     throws Exception {

         try {

             // if we can set the factory, its the first!

             URL.setURLStreamHandlerFactory(factory);

         } catch (Error err) {

             // let's use reflection to get the field holding the factory

             final Field[] fields = URL.class.getDeclaredFields();

             int index = 0;

             Field factoryField = null;

             while ( factoryField == null && index < fields.length ) {

                 final Field current = fields[index];

                 if ( Modifier.isStatic( current.getModifiers() ) && current.getType().equals( URLStreamHandlerFactory.class ) ) {

                     factoryField = current;

                     factoryField.setAccessible(true);

                 } else {

                     index++;

                 }

             }

             if ( factoryField == null ) {

                 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.");

             }

             try {

                 URLStreamHandlerFactory oldFactory = (URLStreamHandlerFactory)factoryField.get(null);

                 if ( factory instanceof ParentAwareURLStreamHandlerFactory ) {

                     ((ParentAwareURLStreamHandlerFactory)factory).setParentFactory(oldFactory);

                 }

                 factoryField.set(null, factory);

             } catch (IllegalArgumentException e) {

                 throw new Exception("Unable to set url stream handler factory " + factory);

             } catch (IllegalAccessException e) {

                 throw new Exception("Unable to set url stream handler factory " + factory);

             }

         }

     }

     protected static Field getStaticURLStreamHandlerFactoryField() {

         Field[] fields = URL.class.getDeclaredFields();

         for ( int i = 0; i < fields.length; i++ ) {

             if ( Modifier.isStatic( fields[i].getModifiers() ) && fields[i].getType().equals( URLStreamHandlerFactory.class ) ) {

                 fields[i].setAccessible( true );

                 return fields[i];

             }

         }

         return null;

     }

 }