Glassfish example source code file (HybridPersistenceProviderResolver.java)

This example Glassfish source code file (HybridPersistenceProviderResolver.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Glassfish tags/keywords

arraylist, arraylist, cachingenabled, classloader, exception, exception, hybridpersistenceproviderresolver, hybridpersistenceproviderresolver, iterator, list, list, log, logging, object, persistenceprovider, string, util

The Glassfish HybridPersistenceProviderResolver.java source code

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright (c) 2010 Oracle and/or its affiliates. All rights reserved.
 *
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * https://glassfish.dev.java.net/public/CDDL+GPL_1_1.html
 * or packager/legal/LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 *
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at packager/legal/LICENSE.txt.
 *
 * GPL Classpath Exception:
 * Oracle designates this particular file as subject to the "Classpath"
 * exception as provided by Oracle in the GPL Version 2 section of the License
 * file that accompanied this code.
 *
 * Modifications:
 * If applicable, add the following below the License Header, with the fields
 * enclosed by brackets [] replaced by your own identifying information:
 * "Portions Copyright [year] [name of copyright owner]"
 *
 * Contributor(s):
 * If you wish your version of this file to be governed by only the CDDL or
 * only the GPL Version 2, indicate your decision by adding "[Contributor]
 * elects to include this software in this distribution under the [CDDL or GPL
 * Version 2] license."  If you don't indicate a single choice of license, a
 * recipient has the option to distribute your version of this file under
 * either the CDDL, the GPL Version 2 or to extend the choice of license to
 * its licensees as provided above.  However, if you add GPL Version 2 code
 * and therefore, elected the GPL Version 2 license, then the option applies
 * only if the new code is made subject to such option by the copyright
 * holder.
 */


package org.glassfish.osgijpa.extension;

import org.glassfish.hk2.osgiresourcelocator.ServiceLoader;

import javax.persistence.spi.PersistenceProvider;
import java.util.*;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * This is a custom implementation of {@link javax.persistence.spi.PersistenceProviderResolver} which has the ability
 * to discover providers that are part of OSGi bundles. As you know, a thread's context loader (TCL) is very widely
 * assumed to represent what an application can see. This is no different in JPA as well. However, there exists some
 * technologies like OSGi, which do not want to rely on Thread's context loader to denote visibility scope of an application.
 * In order to accommodate these diverse technologies, it first attempts to discover providers using TCL.
 * If some providers are visible to the TCL, it considers them as the only set of providers that are supposed to be
 * visible to the current thread and hence returns that list. If TCL can't find any providers, then it assumes that
 * it is invoked in a context which is not relying on TCL to limit visibility, hence  it goes onto discover all providers
 * installed in the current framework. To discover providers installed by OSGi bundles, it currently relies on
 * provider bundles to have META-INF/services/javax.persistence.PersistenceProvider file as every JPA compliant provider
 * bundles such a resource. In future, we can even enhance this class to discover PersistenceProvider service
 * registered by OSGi/JPA compliant bundles.
 * <p/>
 * As per the requirement of JPA spec, this implementation is thread-safe.
 * Please note, this class comes into picture even in Java EE mode usage of JPA via
 * {@link javax.persistence.spi.PersistenceProvider#getProviderUtil()}, which is the only way to call methods like
 * {@link javax.persistence.spi.ProviderUtil#isLoaded(Object)}. So, it is important for this class to be performant.
 * So, this class also supports caching mode which can be explicitly enabled at construction time.
 * Caching should only be enabled in environment where providers are not installed/uninstalled dynamically.
 *
 * @author Sanjeeb.Sahoo@Sun.COM
 */
public class HybridPersistenceProviderResolver implements javax.persistence.spi.PersistenceProviderResolver {
    /*
     * Yes, I am fully aware that eclipselink produced javax.persistence bundle also has an activator
     * which has code to set a custom resolver, but that resolver only works for RFC#143 compliant OSGi JPA providers.
     * So, that does not work for us in GlassFish, as we are really a hybrid environment and our users primarily
     * use JPA in non-OSGi mode. SO, we need this resolver which caters to the need of both kinds of users.
     */

    // Should we hold a WeakReference to provider instead of name of the provider?
    private final Map<ClassLoader, List cl2ProviderNames =
            Collections.synchronizedMap(new WeakHashMap<ClassLoader, List());

    private final boolean cachingEnabled;

    private final Logger logger = Logger.getLogger(getClass().getPackage().getName());

    public HybridPersistenceProviderResolver(boolean cachingEnabled) {
        logger.logp(Level.FINE, "HybridPersistenceProviderResolver", "HybridPersistenceProviderResolver",
                "cachingEnabled = {0}", new Object[]{cachingEnabled});
        this.cachingEnabled = cachingEnabled;
    }

    public List<PersistenceProvider> getPersistenceProviders() {
        ClassLoader cl = Thread.currentThread().getContextClassLoader();
        return getPersistenceProviders(cl);
    }

    private List<PersistenceProvider> getPersistenceProviders(ClassLoader cl) {
        List<PersistenceProvider> providers;
        if (isCachingEnabled()) {
            providers = readCache(cl);
            if (providers == null) {
                providers = discoverPersistenceProviders(cl);
                populateCache(cl, providers);
            }
        } else {
            providers = discoverPersistenceProviders(cl);
        }
        return providers;
    }

    private void populateCache(ClassLoader cl, List<PersistenceProvider> providers) {
        List<String> providerNames = new ArrayList(providers.size());
        providerNames.addAll(convert(providers));
        cl2ProviderNames.put(cl, providerNames);
    }

    private List<PersistenceProvider> readCache(ClassLoader cl) {
        List<String> providerNames = cl2ProviderNames.get(cl);
        return providerNames != null ? convert(providerNames, cl) : null;
    }

    /**
     * Converts a list of provider objects to a list of class names where each name corresponds to provider class name.
     *
     * @param providers list of providers
     * @return list of class names
     */
    private List<String> convert(Iterable providers) {
        List<String> result = new ArrayList();
        for (PersistenceProvider p : providers) {
            result.add(p.getClass().getName());
        }
        return result;
    }

    /**
     * For each name passed in the list, it tries to load the class using the supplied loader, instantiate it
     * and adds it to the list of result object before returning it. If for some reason, the cached provider is
     * no longer available, then it just logs a warning and continues. Since we discover the providers using a single
     * class loader in {@link #discoverPersistenceProviders(ClassLoader)} (ClassLoader)} method,
     * we expect all of them to be loadable using the same loader as well.
     *
     * @param providerNames list of provider class names.
     * @param cl            class loader to be used to load provider classes
     * @return list of provider objects.
     */
    private List<PersistenceProvider> convert(Iterable providerNames, ClassLoader cl) {
        List<PersistenceProvider> result = new ArrayList();
        for (String name : providerNames) {
            try {
                result.add((PersistenceProvider) cl.loadClass(name).newInstance());
            } catch (Exception e) {
                logger.logp(Level.WARNING, "HybridPersistenceProviderResolver", "convert", "Exception trying to instantiate cached provider by name " + name, e);
            }
        }
        return result;
    }

    private List<PersistenceProvider> discoverPersistenceProviders(ClassLoader cl) {
        List<PersistenceProvider> result = new ArrayList();
        if (cl != null) {
            Iterator<PersistenceProvider> services = java.util.ServiceLoader.load(PersistenceProvider.class, cl).iterator();
            while (services.hasNext()) {
                try {
                    PersistenceProvider p = services.next();
                    result.add(p);
                } catch (ServiceConfigurationError e) {
                    // can happen if a cached provider has been uninstalled or something of that sort.
                    logger.logp(Level.FINE, "HybridPersistenceProviderResolver", "getPersistenceProviders", "Exception while discovering providers for class loader " + cl, e);
                }
            }
        }
        if (result.isEmpty()) {
            // Ok, we are called in a context where TCL can't see any provider. e.g.,
            // when an OSGi bundle's activator uses Persistence class. So, discover all providers installed
            // in the framework.
            result.addAll(discoverOSGiProviders());
        }
        return result;
    }

    /**
     * @return persistence providers made available by OSGi bundles installed in the current framework.
     */
    private List<PersistenceProvider> discoverOSGiProviders() {
        List<PersistenceProvider> result = new ArrayList();
        for (PersistenceProvider p : ServiceLoader.lookupProviderInstances(PersistenceProvider.class)) {
            result.add(p);
        }
        return result;
    }

    public synchronized void clearCachedProviders() {
        if (isCachingEnabled()) {
            cl2ProviderNames.clear();
        }
    }

    public boolean isCachingEnabled() {
        return cachingEnabled;
    }

    @Override
    public String toString() {
        return super.toString() + "[CachingEnabled = " + isCachingEnabled() + "]";
    }
}