/*
* Copyright (c) 1999, 2004, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
/*
* Licensed Materials - Property of IBM
* RMI-IIOP v1.0
* Copyright IBM Corp. 1998 1999 All Rights Reserved
*
*/
package org.jboss.com.sun.corba.se.impl.util;
import org.jboss.sun.corba.Bridge;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.Collections;
import java.security.AccessController;
import java.security.PrivilegedAction;
/**
* Utility method for crawling call stack to load class
*/
class JDKClassLoader
{
private static final JDKClassLoaderCache classCache = new JDKClassLoaderCache();
private static final Bridge bridge = AccessController.doPrivileged(new PrivilegedAction<Bridge>()
{
public Bridge run()
{
return Bridge.get();
}
});
static Class<?> loadClass(Class<?> aClass, String className) throws ClassNotFoundException
{
// Maintain the same error semantics as Class.forName()
if (className == null)
{
throw new NullPointerException();
}
if (className.length() == 0)
{
throw new ClassNotFoundException();
}
// It would be nice to bypass JDKClassLoader's attempts completely if it's known that the latest user defined
// ClassLoader will fail.
//
// Otherwise, we end up calling Class.forName here as well as in the next step in JDKBridge. That can take a
// long time depending on the length of the classpath.
// Note: Looking at the only place in JDKBridge where this code is invoked, it is clear that aClass will always
// be null.
ClassLoader loader;
if (aClass != null)
{
loader = aClass.getClassLoader();
}
else
{
loader = bridge.getLatestUserDefinedLoader();
}
// See createKey for a description of what's involved
Object key = classCache.createKey(className, loader);
if (classCache.knownToFail(key))
{
throw new ClassNotFoundException(className);
}
else
{
try
{
// Loading this class with the call stack loader isn't known to fail, so try to load it.
return Class.forName(className, false, loader);
}
catch (ClassNotFoundException cnfe)
{
// Record that we failed to find the class with this particular loader. This way, we won't waste time
// looking with this loader, again.
classCache.recordFailure(key);
throw cnfe;
}
}
}
/**
* Private cache implementation specific to JDKClassLoader.
*/
private static class JDKClassLoaderCache
{
// JDKClassLoader couldn't find the class with the located ClassLoader. Note this in our cache so JDKClassLoader
// can abort early next time.
public final void recordFailure(Object key)
{
cache.put(key, JDKClassLoaderCache.KNOWN_TO_FAIL);
}
// Factory for a key (CacheKey is an implementation detail of JDKClassLoaderCache).
//
// A key currently consists of the class name as well as the latest user defined class loader, so it's fairly
// expensive to create.
public final Object createKey(String className, ClassLoader latestLoader)
{
return new CacheKey(className, latestLoader);
}
// Determine whether or not this combination of class name and ClassLoader is known to fail.
public final boolean knownToFail(Object key)
{
return cache.get(key) == JDKClassLoaderCache.KNOWN_TO_FAIL;
}
// Synchronized WeakHashMap
private final Map<Object, Object> cache = Collections.synchronizedMap(new WeakHashMap<Object, Object>());
// Cache result used to mark the caches when there is no way JDKClassLoader could succeed with the given
// key
private static final Object KNOWN_TO_FAIL = new Object();
// Key consisting of the class name and the latest user defined class loader
private static class CacheKey
{
String className;
ClassLoader loader;
public CacheKey(String className, ClassLoader loader)
{
this.className = className;
this.loader = loader;
}
// Try to incorporate both class name and loader
// into the hashcode
public int hashCode()
{
if (loader == null)
return className.hashCode();
else
return className.hashCode() ^ loader.hashCode();
}
public boolean equals(Object obj)
{
try
{
// WeakHashMap may compare null keys
if (obj == null)
return false;
CacheKey other = (CacheKey) obj;
// I've made a decision to actually compare the loader references. I don't want a case when two
// loader instances override their equals methods and only compare code base.
//
// This way, at worst, our performance will be slower, but we know we'll do the correct loading.
return (className.equals(other.className) && loader == other.loader);
}
catch (ClassCastException cce)
{
return false;
}
}
}
}
}