javax.persistence.spi.PersistenceProviderResolverHolder Maven / Gradle / Ivy
The newest version!
/*******************************************************************************
* Copyright (c) 2008 - 2017 Oracle Corporation. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
* which accompanies this distribution.
* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
* and the Eclipse Distribution License is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*
* Contributors:
* Lukas Jungmann - Java Persistence 2.2
* Linda DeMichiel - Java Persistence 2.1
* Linda DeMichiel - Java Persistence 2.0
*
******************************************************************************/
package javax.persistence.spi;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.ArrayList;
import java.util.List;
import java.util.HashMap;
import java.util.Iterator;
import java.util.ServiceConfigurationError;
import java.util.ServiceLoader;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
* Holds the global {@link javax.persistence.spi.PersistenceProviderResolver}
* instance. If no PersistenceProviderResolver is set by the
* environment, the default PersistenceProviderResolver is used.
*
* Implementations must be thread-safe.
*
* @since Java Persistence 2.0
*/
public class PersistenceProviderResolverHolder {
private static PersistenceProviderResolver singleton = new DefaultPersistenceProviderResolver();
/**
* Returns the current persistence provider resolver.
*
* @return the current persistence provider resolver
*/
public static PersistenceProviderResolver getPersistenceProviderResolver() {
return singleton;
}
/**
* Defines the persistence provider resolver used.
*
* @param resolver persistence provider resolver to be used.
*/
public static void setPersistenceProviderResolver(PersistenceProviderResolver resolver) {
if (resolver == null) {
singleton = new DefaultPersistenceProviderResolver();
} else {
singleton = resolver;
}
}
/**
* Default provider resolver class to use when none is explicitly set.
*
* Uses service loading mechanism as described in the Java Persistence
* specification. A ServiceLoader.load() call is made with the current context
* classloader to find the service provider files on the classpath.
*/
private static class DefaultPersistenceProviderResolver implements PersistenceProviderResolver {
/**
* Cached list of available providers cached by CacheKey to ensure
* there is not potential for provider visibility issues.
*/
private volatile HashMap providers = new HashMap();
/**
* Queue for reference objects referring to class loaders or persistence providers.
*/
private static final ReferenceQueue referenceQueue = new ReferenceQueue();
public List getPersistenceProviders() {
// Before we do the real loading work, see whether we need to
// do some cleanup: If references to class loaders or
// persistence providers have been nulled out, remove all related
// information from the cache.
processQueue();
ClassLoader loader = getContextClassLoader();
CacheKey cacheKey = new CacheKey(loader);
PersistenceProviderReference providersReferent = this.providers.get(cacheKey);
List loadedProviders = null;
if (providersReferent != null) {
loadedProviders = providersReferent.get();
}
if (loadedProviders == null) {
loadedProviders = new ArrayList<>();
Iterator ipp = ServiceLoader.load(PersistenceProvider.class, loader).iterator();
try {
while (ipp.hasNext()) {
try {
PersistenceProvider pp = ipp.next();
loadedProviders.add(pp);
} catch (ServiceConfigurationError sce) {
log(Level.FINEST, sce.toString());
}
}
} catch (ServiceConfigurationError sce) {
log(Level.FINEST, sce.toString());
}
// If none are found we'll log the provider names for diagnostic
// purposes.
if (loadedProviders.isEmpty()) {
log(Level.WARNING, "No valid providers found.");
}
providersReferent = new PersistenceProviderReference(loadedProviders, referenceQueue, cacheKey);
this.providers.put(cacheKey, providersReferent);
}
return loadedProviders;
}
/**
* Remove garbage collected cache keys & providers.
*/
private void processQueue() {
CacheKeyReference ref;
while ((ref = (CacheKeyReference) referenceQueue.poll()) != null) {
providers.remove(ref.getCacheKey());
}
}
/**
* Wraps Thread.currentThread().getContextClassLoader() into a doPrivileged block if security manager is present
*/
private static ClassLoader getContextClassLoader() {
if (System.getSecurityManager() == null) {
return Thread.currentThread().getContextClassLoader();
} else {
return AccessController.doPrivileged(new PrivilegedAction() {
public ClassLoader run() {
return Thread.currentThread().getContextClassLoader();
}
});
}
}
private static final String LOGGER_SUBSYSTEM = "javax.persistence.spi";
private Logger logger;
private void log(Level level, String message) {
if (this.logger == null) {
this.logger = Logger.getLogger(LOGGER_SUBSYSTEM);
}
this.logger.log(level, LOGGER_SUBSYSTEM + "::" + message);
}
/**
* Clear all cached providers
*/
public void clearCachedProviders() {
this.providers.clear();
}
/**
* The common interface to get a CacheKey implemented by
* LoaderReference and PersistenceProviderReference.
*/
private interface CacheKeyReference {
public CacheKey getCacheKey();
}
/**
* Key used for cached persistence providers. The key checks
* the class loader to determine if the persistence providers
* is a match to the requested one. The loader may be null.
*/
private class CacheKey implements Cloneable {
/* Weak Reference to ClassLoader */
private LoaderReference loaderRef;
/* Cached Hashcode */
private int hashCodeCache;
CacheKey(ClassLoader loader) {
if (loader == null) {
this.loaderRef = null;
} else {
loaderRef = new LoaderReference(loader, referenceQueue, this);
}
calculateHashCode();
}
ClassLoader getLoader() {
return (loaderRef != null) ? loaderRef.get() : null;
}
public boolean equals(Object other) {
if (this == other) {
return true;
}
try {
final CacheKey otherEntry = (CacheKey) other;
// quick check to see if they are not equal
if (hashCodeCache != otherEntry.hashCodeCache) {
return false;
}
// are refs (both non-null) or (both null)?
if (loaderRef == null) {
return otherEntry.loaderRef == null;
}
ClassLoader loader = loaderRef.get();
return (otherEntry.loaderRef != null)
// with a null reference we can no longer find
// out which class loader was referenced; so
// treat it as unequal
&& (loader != null) && (loader == otherEntry.loaderRef.get());
} catch (NullPointerException e) {
} catch (ClassCastException e) {
}
return false;
}
public int hashCode() {
return hashCodeCache;
}
private void calculateHashCode() {
ClassLoader loader = getLoader();
if (loader != null) {
hashCodeCache = loader.hashCode();
}
}
public Object clone() {
try {
CacheKey clone = (CacheKey) super.clone();
if (loaderRef != null) {
clone.loaderRef = new LoaderReference(loaderRef.get(), referenceQueue, clone);
}
return clone;
} catch (CloneNotSupportedException e) {
// this should never happen
throw new InternalError();
}
}
public String toString() {
return "CacheKey[" + getLoader() + ")]";
}
}
/**
* References to class loaders are weak references, so that they can be
* garbage collected when nobody else is using them. The DefaultPersistenceProviderResolver
* class has no reason to keep class loaders alive.
*/
private class LoaderReference extends WeakReference
implements CacheKeyReference {
private CacheKey cacheKey;
@SuppressWarnings("unchecked")
LoaderReference(ClassLoader referent, ReferenceQueue q, CacheKey key) {
super(referent, q);
cacheKey = key;
}
public CacheKey getCacheKey() {
return cacheKey;
}
}
/**
* References to persistence provider are soft references so that they can be garbage
* collected when they have no hard references.
*/
private class PersistenceProviderReference extends SoftReference>
implements CacheKeyReference {
private CacheKey cacheKey;
@SuppressWarnings("unchecked")
PersistenceProviderReference(List referent, ReferenceQueue q, CacheKey key) {
super(referent, q);
cacheKey = key;
}
public CacheKey getCacheKey() {
return cacheKey;
}
}
}
}