/*
* Copyright 1999-2004 Sun Microsystems, Inc. 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. Sun designates this
* particular file as subject to the "Classpath" exception as provided
* by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
* CA 95054 USA or visit www.sun.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 com.sun.corba.se.impl.util;
import 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 =
(Bridge)AccessController.doPrivileged(
new PrivilegedAction() {
public Object 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 cache
= Collections.synchronizedMap(new WeakHashMap());
// 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;
}
}
}
}
}