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The Injector.java Java example source code
/*
* Copyright (c) 1997, 2013, 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.
*/
package com.sun.xml.internal.bind.v2.runtime.reflect.opt;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.ref.WeakReference;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.HashMap;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.logging.Level;
import java.util.logging.Logger;
import com.sun.xml.internal.bind.Util;
import com.sun.xml.internal.bind.v2.runtime.reflect.Accessor;
/**
* A {@link ClassLoader} used to "inject" optimized accessor classes
* into the VM.
*
* <p>
* Its parent class loader needs to be set to the one that can see the user
* class.
*
* @author Kohsuke Kawaguchi
*/
final class Injector {
/**
* {@link Injector}s keyed by their parent {@link ClassLoader}.
*
* We only need one injector per one user class loader.
*/
private static final ReentrantReadWriteLock irwl = new ReentrantReadWriteLock();
private static final Lock ir = irwl.readLock();
private static final Lock iw = irwl.writeLock();
private static final Map<ClassLoader, WeakReference injectors =
new WeakHashMap<ClassLoader, WeakReference();
private static final Logger logger = Util.getClassLogger();
/**
* Injects a new class into the given class loader.
*
* @return null
* if it fails to inject.
*/
static Class inject(ClassLoader cl, String className, byte[] image) {
Injector injector = get(cl);
if (injector != null) {
return injector.inject(className, image);
} else {
return null;
}
}
/**
* Returns the already injected class, or null.
*/
static Class find(ClassLoader cl, String className) {
Injector injector = get(cl);
if (injector != null) {
return injector.find(className);
} else {
return null;
}
}
/**
* Gets or creates an {@link Injector} for the given class loader.
*
* @return null
* if it fails.
*/
private static Injector get(ClassLoader cl) {
Injector injector = null;
WeakReference<Injector> wr;
ir.lock();
try {
wr = injectors.get(cl);
} finally {
ir.unlock();
}
if (wr != null) {
injector = wr.get();
}
if (injector == null) {
try {
wr = new WeakReference<Injector>(injector = new Injector(cl));
iw.lock();
try {
if (!injectors.containsKey(cl)) {
injectors.put(cl, wr);
}
} finally {
iw.unlock();
}
} catch (SecurityException e) {
logger.log(Level.FINE, "Unable to set up a back-door for the injector", e);
return null;
}
}
return injector;
}
/**
* Injected classes keyed by their names.
*/
private final Map<String, Class> classes = new HashMap();
private final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();
private final Lock r = rwl.readLock();
private final Lock w = rwl.writeLock();
private final ClassLoader parent;
/**
* True if this injector is capable of injecting accessors.
* False otherwise, which happens if this classloader can't see {@link Accessor}.
*/
private final boolean loadable;
private static final Method defineClass;
private static final Method resolveClass;
private static final Method findLoadedClass;
static {
try {
defineClass = ClassLoader.class.getDeclaredMethod("defineClass", String.class, byte[].class, Integer.TYPE, Integer.TYPE);
resolveClass = ClassLoader.class.getDeclaredMethod("resolveClass", Class.class);
findLoadedClass = ClassLoader.class.getDeclaredMethod("findLoadedClass", String.class);
} catch (NoSuchMethodException e) {
// impossible
throw new NoSuchMethodError(e.getMessage());
}
AccessController.doPrivileged(new PrivilegedAction<Void>() {
@Override
public Void run() {
// TODO: check security implication
// do these setAccessible allow anyone to call these methods freely?s
defineClass.setAccessible(true);
resolveClass.setAccessible(true);
findLoadedClass.setAccessible(true);
return null;
}
});
}
private Injector(ClassLoader parent) {
this.parent = parent;
assert parent != null;
boolean loadableCheck = false;
try {
loadableCheck = parent.loadClass(Accessor.class.getName()) == Accessor.class;
} catch (ClassNotFoundException e) {
// not loadable
}
this.loadable = loadableCheck;
}
@SuppressWarnings("LockAcquiredButNotSafelyReleased")
private Class inject(String className, byte[] image) {
if (!loadable) // this injector cannot inject anything
{
return null;
}
boolean wlocked = false;
boolean rlocked = false;
try {
r.lock();
rlocked = true;
Class c = classes.get(className);
// Unlock now during the findLoadedClass process to avoid
// deadlocks
r.unlock();
rlocked = false;
//find loaded class from classloader
if (c == null) {
try {
c = (Class) findLoadedClass.invoke(parent, className.replace('/', '.'));
} catch (IllegalArgumentException e) {
logger.log(Level.FINE, "Unable to find " + className, e);
} catch (IllegalAccessException e) {
logger.log(Level.FINE, "Unable to find " + className, e);
} catch (InvocationTargetException e) {
Throwable t = e.getTargetException();
logger.log(Level.FINE, "Unable to find " + className, t);
}
if (c != null) {
w.lock();
wlocked = true;
classes.put(className, c);
w.unlock();
wlocked = false;
return c;
}
}
if (c == null) {
r.lock();
rlocked = true;
c = classes.get(className);
// Unlock now during the define/resolve process to avoid
// deadlocks
r.unlock();
rlocked = false;
if (c == null) {
// we need to inject a class into the
try {
c = (Class) defineClass.invoke(parent, className.replace('/', '.'), image, 0, image.length);
resolveClass.invoke(parent, c);
} catch (IllegalAccessException e) {
logger.log(Level.FINE, "Unable to inject " + className, e);
return null;
} catch (InvocationTargetException e) {
Throwable t = e.getTargetException();
if (t instanceof LinkageError) {
logger.log(Level.FINE, "duplicate class definition bug occured? Please report this : " + className, t);
} else {
logger.log(Level.FINE, "Unable to inject " + className, t);
}
return null;
} catch (SecurityException e) {
logger.log(Level.FINE, "Unable to inject " + className, e);
return null;
} catch (LinkageError e) {
logger.log(Level.FINE, "Unable to inject " + className, e);
return null;
}
w.lock();
wlocked = true;
// During the time we were unlocked, we could have tried to
// load the class from more than one thread. Check now to see
// if someone else beat us to registering this class
if (!classes.containsKey(className)) {
classes.put(className, c);
}
w.unlock();
wlocked = false;
}
}
return c;
} finally {
if (rlocked) {
r.unlock();
}
if (wlocked) {
w.unlock();
}
}
}
private Class find(String className) {
r.lock();
try {
return classes.get(className);
} finally {
r.unlock();
}
}
}
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