/*
* Copyright 2001-2009 Terracotta, Inc.
*
* Licensed 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.quartz.simpl;
import java.util.Iterator;
import java.util.LinkedList;
import java.net.URL;
import java.io.InputStream;
import org.quartz.spi.ClassLoadHelper;
/**
* A <code>ClassLoadHelper</code> uses all of the <code>ClassLoadHelper</code>
* types that are found in this package in its attempts to load a class, when
* one scheme is found to work, it is promoted to the scheme that will be used
* first the next time a class is loaded (in order to improve performance).
*
* <p>
* This approach is used because of the wide variance in class loader behavior
* between the various environments in which Quartz runs (e.g. disparate
* application servers, stand-alone, mobile devices, etc.). Because of this
* disparity, Quartz ran into difficulty with a one class-load style fits-all
* design. Thus, this class loader finds the approach that works, then
* 'remembers' it.
* </p>
*
* @see org.quartz.spi.ClassLoadHelper
* @see org.quartz.simpl.LoadingLoaderClassLoadHelper
* @see org.quartz.simpl.SimpleClassLoadHelper
* @see org.quartz.simpl.ThreadContextClassLoadHelper
* @see org.quartz.simpl.InitThreadContextClassLoadHelper
*
* @author jhouse
* @author pl47ypus
*/
public class CascadingClassLoadHelper implements ClassLoadHelper {
/*
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* Data members.
*
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*/
private LinkedList loadHelpers;
private ClassLoadHelper bestCandidate;
/*
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* Interface.
*
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*/
/**
* Called to give the ClassLoadHelper a chance to initialize itself,
* including the opportunity to "steal" the class loader off of the calling
* thread, which is the thread that is initializing Quartz.
*/
public void initialize() {
loadHelpers = new LinkedList();
loadHelpers.add(new LoadingLoaderClassLoadHelper());
loadHelpers.add(new SimpleClassLoadHelper());
loadHelpers.add(new ThreadContextClassLoadHelper());
loadHelpers.add(new InitThreadContextClassLoadHelper());
Iterator iter = loadHelpers.iterator();
while (iter.hasNext()) {
ClassLoadHelper loadHelper = (ClassLoadHelper) iter.next();
loadHelper.initialize();
}
}
/**
* Return the class with the given name.
*/
public Class loadClass(String name) throws ClassNotFoundException {
if (bestCandidate != null) {
try {
return bestCandidate.loadClass(name);
} catch (Exception e) {
bestCandidate = null;
}
}
ClassNotFoundException cnfe = null;
Class clazz = null;
ClassLoadHelper loadHelper = null;
Iterator iter = loadHelpers.iterator();
while (iter.hasNext()) {
loadHelper = (ClassLoadHelper) iter.next();
try {
clazz = loadHelper.loadClass(name);
break;
} catch (ClassNotFoundException e) {
cnfe = e;
}
}
if (clazz == null) {
throw cnfe;
}
bestCandidate = loadHelper;
return clazz;
}
/**
* Finds a resource with a given name. This method returns null if no
* resource with this name is found.
* @param name name of the desired resource
* @return a java.net.URL object
*/
public URL getResource(String name) {
if (bestCandidate != null) {
try {
return bestCandidate.getResource(name);
} catch (Exception e) {
bestCandidate = null;
}
}
URL result = null;
ClassLoadHelper loadHelper = null;
Iterator iter = loadHelpers.iterator();
while (iter.hasNext()) {
loadHelper = (ClassLoadHelper) iter.next();
result = loadHelper.getResource(name);
if (result != null) {
break;
}
}
bestCandidate = loadHelper;
return result;
}
/**
* Finds a resource with a given name. This method returns null if no
* resource with this name is found.
* @param name name of the desired resource
* @return a java.io.InputStream object
*/
public InputStream getResourceAsStream(String name) {
if (bestCandidate != null) {
try {
return bestCandidate.getResourceAsStream(name);
} catch (Exception e) {
bestCandidate = null;
}
}
InputStream result = null;
ClassLoadHelper loadHelper = null;
Iterator iter = loadHelpers.iterator();
while (iter.hasNext()) {
loadHelper = (ClassLoadHelper) iter.next();
result = loadHelper.getResourceAsStream(name);
if (result != null) {
break;
}
}
bestCandidate = loadHelper;
return result;
}
/**
* Enable sharing of the class-loader with 3rd party (e.g. digester).
*
* @return the class-loader user be the helper.
*/
public ClassLoader getClassLoader() {
return (this.bestCandidate == null) ?
Thread.currentThread().getContextClassLoader() :
this.bestCandidate.getClassLoader();
}
}