/*
 * Copyright 2002-2020 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.orm.jpa;

import java.io.IOException;
import java.io.NotSerializableException;
import java.io.ObjectInputStream;
import java.io.ObjectStreamException;
import java.io.Serializable;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.HashMap;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.Properties;
import java.util.Set;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.PersistenceException;
import javax.persistence.Query;
import javax.persistence.SynchronizationType;
import javax.persistence.spi.PersistenceProvider;
import javax.persistence.spi.PersistenceUnitInfo;
import javax.sql.DataSource;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.beans.BeanUtils;
import org.springframework.beans.factory.BeanClassLoaderAware;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.BeanNameAware;
import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.core.task.AsyncTaskExecutor;
import org.springframework.dao.DataAccessException;
import org.springframework.dao.support.PersistenceExceptionTranslator;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.CollectionUtils;

/**
 * Abstract {@link org.springframework.beans.factory.FactoryBean} that creates
 * a local JPA {@link javax.persistence.EntityManagerFactory} instance within
 * a Spring application context.
 *
 * <p>Encapsulates the common functionality between the different JPA bootstrap
 * contracts (standalone as well as container).
 *
 * <p>Implements support for standard JPA configuration conventions as well as
 * Spring's customizable {@link JpaVendorAdapter} mechanism, and controls the
 * EntityManagerFactory's lifecycle.
 *
 * <p>This class also implements the
 * {@link org.springframework.dao.support.PersistenceExceptionTranslator}
 * interface, as autodetected by Spring's
 * {@link org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor},
 * for AOP-based translation of native exceptions to Spring DataAccessExceptions.
 * Hence, the presence of e.g. LocalEntityManagerFactoryBean automatically enables
 * a PersistenceExceptionTranslationPostProcessor to translate JPA exceptions.
 *
 * @author Juergen Hoeller
 * @author Rod Johnson
 * @since 2.0
 * @see LocalEntityManagerFactoryBean
 * @see LocalContainerEntityManagerFactoryBean
 */
@SuppressWarnings("serial")
public abstract class AbstractEntityManagerFactoryBean implements
                FactoryBean<EntityManagerFactory>, BeanClassLoaderAware, BeanFactoryAware, BeanNameAware,
                InitializingBean, DisposableBean, EntityManagerFactoryInfo, PersistenceExceptionTranslator, Serializable {

        /** Logger available to subclasses. */
        protected final Log logger = LogFactory.getLog(getClass());

        @Nullable
        private PersistenceProvider persistenceProvider;

        @Nullable
        private String persistenceUnitName;

        private final Map<String, Object> jpaPropertyMap = new HashMap<>();

        @Nullable
        private Class<? extends EntityManagerFactory> entityManagerFactoryInterface;

        @Nullable
        private Class<? extends EntityManager> entityManagerInterface;

        @Nullable
        private JpaDialect jpaDialect;

        @Nullable
        private JpaVendorAdapter jpaVendorAdapter;

        @Nullable
        private AsyncTaskExecutor bootstrapExecutor;

        private ClassLoader beanClassLoader = getClass().getClassLoader();

        @Nullable
        private BeanFactory beanFactory;

        @Nullable
        private String beanName;

        /** Raw EntityManagerFactory as returned by the PersistenceProvider. */
        @Nullable
        private EntityManagerFactory nativeEntityManagerFactory;

        /** Future for lazily initializing raw target EntityManagerFactory. */
        @Nullable
        private Future<EntityManagerFactory> nativeEntityManagerFactoryFuture;

        /** Exposed client-level EntityManagerFactory proxy. */
        @Nullable
        private EntityManagerFactory entityManagerFactory;


        /**
         * Set the PersistenceProvider implementation class to use for creating the
         * EntityManagerFactory. If not specified, the persistence provider will be
         * taken from the JpaVendorAdapter (if any) or retrieved through scanning
         * (as far as possible).
         * @see JpaVendorAdapter#getPersistenceProvider()
         * @see javax.persistence.spi.PersistenceProvider
         * @see javax.persistence.Persistence
         */
        public void setPersistenceProviderClass(Class<? extends PersistenceProvider> persistenceProviderClass) {
                this.persistenceProvider = BeanUtils.instantiateClass(persistenceProviderClass);
        }

        /**
         * Set the PersistenceProvider instance to use for creating the
         * EntityManagerFactory. If not specified, the persistence provider
         * will be taken from the JpaVendorAdapter (if any) or determined
         * by the persistence unit deployment descriptor (as far as possible).
         * @see JpaVendorAdapter#getPersistenceProvider()
         * @see javax.persistence.spi.PersistenceProvider
         * @see javax.persistence.Persistence
         */
        public void setPersistenceProvider(@Nullable PersistenceProvider persistenceProvider) {
                this.persistenceProvider = persistenceProvider;
        }

        @Override
        @Nullable
        public PersistenceProvider getPersistenceProvider() {
                return this.persistenceProvider;
        }

        /**
         * Specify the name of the EntityManagerFactory configuration.
         * <p>Default is none, indicating the default EntityManagerFactory
         * configuration. The persistence provider will throw an exception if
         * ambiguous EntityManager configurations are found.
         * @see javax.persistence.Persistence#createEntityManagerFactory(String)
         */
        public void setPersistenceUnitName(@Nullable String persistenceUnitName) {
                this.persistenceUnitName = persistenceUnitName;
        }

        @Override
        @Nullable
        public String getPersistenceUnitName() {
                return this.persistenceUnitName;
        }

        /**
         * Specify JPA properties, to be passed into
         * {@code Persistence.createEntityManagerFactory} (if any).
         * <p>Can be populated with a String "value" (parsed via PropertiesEditor) or a
         * "props" element in XML bean definitions.
         * @see javax.persistence.Persistence#createEntityManagerFactory(String, Map)
         * @see javax.persistence.spi.PersistenceProvider#createContainerEntityManagerFactory(PersistenceUnitInfo, Map)
         */
        public void setJpaProperties(Properties jpaProperties) {
                CollectionUtils.mergePropertiesIntoMap(jpaProperties, this.jpaPropertyMap);
        }

        /**
         * Specify JPA properties as a Map, to be passed into
         * {@code Persistence.createEntityManagerFactory} (if any).
         * <p>Can be populated with a "map" or "props" element in XML bean definitions.
         * @see javax.persistence.Persistence#createEntityManagerFactory(String, Map)
         * @see javax.persistence.spi.PersistenceProvider#createContainerEntityManagerFactory(PersistenceUnitInfo, Map)
         */
        public void setJpaPropertyMap(@Nullable Map<String, ?> jpaProperties) {
                if (jpaProperties != null) {
                        this.jpaPropertyMap.putAll(jpaProperties);
                }
        }

        /**
         * Allow Map access to the JPA properties to be passed to the persistence
         * provider, with the option to add or override specific entries.
         * <p>Useful for specifying entries directly, for example via
         * "jpaPropertyMap[myKey]".
         */
        public Map<String, Object> getJpaPropertyMap() {
                return this.jpaPropertyMap;
        }

        /**
         * Specify the (potentially vendor-specific) EntityManagerFactory interface
         * that this EntityManagerFactory proxy is supposed to implement.
         * <p>The default will be taken from the specific JpaVendorAdapter, if any,
         * or set to the standard {@code javax.persistence.EntityManagerFactory}
         * interface else.
         * @see JpaVendorAdapter#getEntityManagerFactoryInterface()
         */
        public void setEntityManagerFactoryInterface(Class<? extends EntityManagerFactory> emfInterface) {
                this.entityManagerFactoryInterface = emfInterface;
        }

        /**
         * Specify the (potentially vendor-specific) EntityManager interface
         * that this factory's EntityManagers are supposed to implement.
         * <p>The default will be taken from the specific JpaVendorAdapter, if any,
         * or set to the standard {@code javax.persistence.EntityManager}
         * interface else.
         * @see JpaVendorAdapter#getEntityManagerInterface()
         * @see EntityManagerFactoryInfo#getEntityManagerInterface()
         */
        public void setEntityManagerInterface(@Nullable Class<? extends EntityManager> emInterface) {
                this.entityManagerInterface = emInterface;
        }

        @Override
        @Nullable
        public Class<? extends EntityManager> getEntityManagerInterface() {
                return this.entityManagerInterface;
        }

        /**
         * Specify the vendor-specific JpaDialect implementation to associate with
         * this EntityManagerFactory. This will be exposed through the
         * EntityManagerFactoryInfo interface, to be picked up as default dialect by
         * accessors that intend to use JpaDialect functionality.
         * @see EntityManagerFactoryInfo#getJpaDialect()
         */
        public void setJpaDialect(@Nullable JpaDialect jpaDialect) {
                this.jpaDialect = jpaDialect;
        }

        @Override
        @Nullable
        public JpaDialect getJpaDialect() {
                return this.jpaDialect;
        }

        /**
         * Specify the JpaVendorAdapter implementation for the desired JPA provider,
         * if any. This will initialize appropriate defaults for the given provider,
         * such as persistence provider class and JpaDialect, unless locally
         * overridden in this FactoryBean.
         */
        public void setJpaVendorAdapter(@Nullable JpaVendorAdapter jpaVendorAdapter) {
                this.jpaVendorAdapter = jpaVendorAdapter;
        }

        /**
         * Return the JpaVendorAdapter implementation for this EntityManagerFactory,
         * or {@code null} if not known.
         */
        @Nullable
        public JpaVendorAdapter getJpaVendorAdapter() {
                return this.jpaVendorAdapter;
        }

        /**
         * Specify an asynchronous executor for background bootstrapping,
         * e.g. a {@link org.springframework.core.task.SimpleAsyncTaskExecutor}.
         * <p>{@code EntityManagerFactory} initialization will then switch into background
         * bootstrap mode, with a {@code EntityManagerFactory} proxy immediately returned for
         * injection purposes instead of waiting for the JPA provider's bootstrapping to complete.
         * However, note that the first actual call to a {@code EntityManagerFactory} method will
         * then block until the JPA provider's bootstrapping completed, if not ready by then.
         * For maximum benefit, make sure to avoid early {@code EntityManagerFactory} calls
         * in init methods of related beans, even for metadata introspection purposes.
         * @since 4.3
         */
        public void setBootstrapExecutor(@Nullable AsyncTaskExecutor bootstrapExecutor) {
                this.bootstrapExecutor = bootstrapExecutor;
        }

        /**
         * Return the asynchronous executor for background bootstrapping, if any.
         * @since 4.3
         */
        @Nullable
        public AsyncTaskExecutor getBootstrapExecutor() {
                return this.bootstrapExecutor;
        }

        @Override
        public void setBeanClassLoader(ClassLoader classLoader) {
                this.beanClassLoader = classLoader;
        }

        @Override
        public ClassLoader getBeanClassLoader() {
                return this.beanClassLoader;
        }

        @Override
        public void setBeanFactory(BeanFactory beanFactory) {
                this.beanFactory = beanFactory;
        }

        @Override
        public void setBeanName(String name) {
                this.beanName = name;
        }


        @Override
        public void afterPropertiesSet() throws PersistenceException {
                JpaVendorAdapter jpaVendorAdapter = getJpaVendorAdapter();
                if (jpaVendorAdapter != null) {
                        if (this.persistenceProvider == null) {
                                this.persistenceProvider = jpaVendorAdapter.getPersistenceProvider();
                        }
                        PersistenceUnitInfo pui = getPersistenceUnitInfo();
                        Map<String, ?> vendorPropertyMap = (pui != null ? jpaVendorAdapter.getJpaPropertyMap(pui) :
                                        jpaVendorAdapter.getJpaPropertyMap());
                        if (!CollectionUtils.isEmpty(vendorPropertyMap)) {
                                vendorPropertyMap.forEach((key, value) -> {
                                        if (!this.jpaPropertyMap.containsKey(key)) {
                                                this.jpaPropertyMap.put(key, value);
                                        }
                                });
                        }
                        if (this.entityManagerFactoryInterface == null) {
                                this.entityManagerFactoryInterface = jpaVendorAdapter.getEntityManagerFactoryInterface();
                                if (!ClassUtils.isVisible(this.entityManagerFactoryInterface, this.beanClassLoader)) {
                                        this.entityManagerFactoryInterface = EntityManagerFactory.class;
                                }
                        }
                        if (this.entityManagerInterface == null) {
                                this.entityManagerInterface = jpaVendorAdapter.getEntityManagerInterface();
                                if (!ClassUtils.isVisible(this.entityManagerInterface, this.beanClassLoader)) {
                                        this.entityManagerInterface = EntityManager.class;
                                }
                        }
                        if (this.jpaDialect == null) {
                                this.jpaDialect = jpaVendorAdapter.getJpaDialect();
                        }
                }

                AsyncTaskExecutor bootstrapExecutor = getBootstrapExecutor();
                if (bootstrapExecutor != null) {
                        this.nativeEntityManagerFactoryFuture = bootstrapExecutor.submit(this::buildNativeEntityManagerFactory);
                }
                else {
                        this.nativeEntityManagerFactory = buildNativeEntityManagerFactory();
                }

                // Wrap the EntityManagerFactory in a factory implementing all its interfaces.
                // This allows interception of createEntityManager methods to return an
                // application-managed EntityManager proxy that automatically joins
                // existing transactions.
                this.entityManagerFactory = createEntityManagerFactoryProxy(this.nativeEntityManagerFactory);
        }

        private EntityManagerFactory buildNativeEntityManagerFactory() {
                EntityManagerFactory emf;
                try {
                        emf = createNativeEntityManagerFactory();
                }
                catch (PersistenceException ex) {
                        if (ex.getClass() == PersistenceException.class) {
                                // Plain PersistenceException wrapper for underlying exception?
                                // Make sure the nested exception message is properly exposed,
                                // along the lines of Spring's NestedRuntimeException.getMessage()
                                Throwable cause = ex.getCause();
                                if (cause != null) {
                                        String message = ex.getMessage();
                                        String causeString = cause.toString();
                                        if (!message.endsWith(causeString)) {
                                                ex = new PersistenceException(message + "; nested exception is " + causeString, cause);
                                        }
                                }
                        }
                        if (logger.isErrorEnabled()) {
                                logger.error("Failed to initialize JPA EntityManagerFactory: " + ex.getMessage());
                        }
                        throw ex;
                }

                JpaVendorAdapter jpaVendorAdapter = getJpaVendorAdapter();
                if (jpaVendorAdapter != null) {
                        jpaVendorAdapter.postProcessEntityManagerFactory(emf);
                }

                if (logger.isInfoEnabled()) {
                        logger.info("Initialized JPA EntityManagerFactory for persistence unit '" + getPersistenceUnitName() + "'");
                }
                return emf;
        }

        /**
         * Create a proxy for the given {@link EntityManagerFactory}. We do this to be able to
         * return a transaction-aware proxy for an application-managed {@link EntityManager}.
         * @param emf the EntityManagerFactory as returned by the persistence provider,
         * if initialized already
         * @return the EntityManagerFactory proxy
         */
        protected EntityManagerFactory createEntityManagerFactoryProxy(@Nullable EntityManagerFactory emf) {
                Set<Class<?>> ifcs = new LinkedHashSet<>();
                Class<?> entityManagerFactoryInterface = this.entityManagerFactoryInterface;
                if (entityManagerFactoryInterface != null) {
                        ifcs.add(entityManagerFactoryInterface);
                }
                else if (emf != null) {
                        ifcs.addAll(ClassUtils.getAllInterfacesForClassAsSet(emf.getClass(), this.beanClassLoader));
                }
                else {
                        ifcs.add(EntityManagerFactory.class);
                }
                ifcs.add(EntityManagerFactoryInfo.class);

                try {
                        return (EntityManagerFactory) Proxy.newProxyInstance(this.beanClassLoader,
                                        ClassUtils.toClassArray(ifcs), new ManagedEntityManagerFactoryInvocationHandler(this));
                }
                catch (IllegalArgumentException ex) {
                        if (entityManagerFactoryInterface != null) {
                                throw new IllegalStateException("EntityManagerFactory interface [" + entityManagerFactoryInterface +
                                                "] seems to conflict with Spring's EntityManagerFactoryInfo mixin - consider resetting the "+
                                                "'entityManagerFactoryInterface' property to plain [javax.persistence.EntityManagerFactory]", ex);
                        }
                        else {
                                throw new IllegalStateException("Conflicting EntityManagerFactory interfaces - " +
                                                "consider specifying the 'jpaVendorAdapter' or 'entityManagerFactoryInterface' property " +
                                                "to select a specific EntityManagerFactory interface to proceed with", ex);
                        }
                }
        }

        /**
         * Delegate an incoming invocation from the proxy, dispatching to EntityManagerFactoryInfo
         * or the native EntityManagerFactory accordingly.
         */
        Object invokeProxyMethod(Method method, @Nullable Object[] args) throws Throwable {
                if (method.getDeclaringClass().isAssignableFrom(EntityManagerFactoryInfo.class)) {
                        return method.invoke(this, args);
                }
                else if (method.getName().equals("createEntityManager") && args != null && args.length > 0 &&
                                args[0] == SynchronizationType.SYNCHRONIZED) {
                        // JPA 2.1's createEntityManager(SynchronizationType, Map)
                        // Redirect to plain createEntityManager and add synchronization semantics through Spring proxy
                        EntityManager rawEntityManager = (args.length > 1 ?
                                        getNativeEntityManagerFactory().createEntityManager((Map<?, ?>) args[1]) :
                                        getNativeEntityManagerFactory().createEntityManager());
                        return ExtendedEntityManagerCreator.createApplicationManagedEntityManager(rawEntityManager, this, true);
                }

                // Look for Query arguments, primarily JPA 2.1's addNamedQuery(String, Query)
                if (args != null) {
                        for (int i = 0; i < args.length; i++) {
                                Object arg = args[i];
                                if (arg instanceof Query && Proxy.isProxyClass(arg.getClass())) {
                                        // Assumably a Spring-generated proxy from SharedEntityManagerCreator:
                                        // since we're passing it back to the native EntityManagerFactory,
                                        // let's unwrap it to the original Query object from the provider.
                                        try {
                                                args[i] = ((Query) arg).unwrap(null);
                                        }
                                        catch (RuntimeException ex) {
                                                // Ignore - simply proceed with given Query object then
                                        }
                                }
                        }
                }

                // Standard delegation to the native factory, just post-processing EntityManager return values
                Object retVal = method.invoke(getNativeEntityManagerFactory(), args);
                if (retVal instanceof EntityManager) {
                        // Any other createEntityManager variant - expecting non-synchronized semantics
                        EntityManager rawEntityManager = (EntityManager) retVal;
                        retVal = ExtendedEntityManagerCreator.createApplicationManagedEntityManager(rawEntityManager, this, false);
                }
                return retVal;
        }

        /**
         * Subclasses must implement this method to create the EntityManagerFactory
         * that will be returned by the {@code getObject()} method.
         * @return the EntityManagerFactory instance returned by this FactoryBean
         * @throws PersistenceException if the EntityManager cannot be created
         */
        protected abstract EntityManagerFactory createNativeEntityManagerFactory() throws PersistenceException;


        /**
         * Implementation of the PersistenceExceptionTranslator interface, as
         * autodetected by Spring's PersistenceExceptionTranslationPostProcessor.
         * <p>Uses the dialect's conversion if possible; otherwise falls back to
         * standard JPA exception conversion.
         * @see org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor
         * @see JpaDialect#translateExceptionIfPossible
         * @see EntityManagerFactoryUtils#convertJpaAccessExceptionIfPossible
         */
        @Override
        @Nullable
        public DataAccessException translateExceptionIfPossible(RuntimeException ex) {
                JpaDialect jpaDialect = getJpaDialect();
                return (jpaDialect != null ? jpaDialect.translateExceptionIfPossible(ex) :
                                EntityManagerFactoryUtils.convertJpaAccessExceptionIfPossible(ex));
        }

        @Override
        public EntityManagerFactory getNativeEntityManagerFactory() {
                if (this.nativeEntityManagerFactory != null) {
                        return this.nativeEntityManagerFactory;
                }
                else {
                        Assert.state(this.nativeEntityManagerFactoryFuture != null, "No native EntityManagerFactory available");
                        try {
                                return this.nativeEntityManagerFactoryFuture.get();
                        }
                        catch (InterruptedException ex) {
                                Thread.currentThread().interrupt();
                                throw new IllegalStateException("Interrupted during initialization of native EntityManagerFactory", ex);
                        }
                        catch (ExecutionException ex) {
                                Throwable cause = ex.getCause();
                                if (cause instanceof PersistenceException) {
                                        // Rethrow a provider configuration exception (possibly with a nested cause) directly
                                        throw (PersistenceException) cause;
                                }
                                throw new IllegalStateException("Failed to asynchronously initialize native EntityManagerFactory: " +
                                                ex.getMessage(), cause);
                        }
                }
        }

        @Override
        @Nullable
        public PersistenceUnitInfo getPersistenceUnitInfo() {
                return null;
        }

        @Override
        @Nullable
        public DataSource getDataSource() {
                return null;
        }


        /**
         * Return the singleton EntityManagerFactory.
         */
        @Override
        @Nullable
        public EntityManagerFactory getObject() {
                return this.entityManagerFactory;
        }

        @Override
        public Class<? extends EntityManagerFactory> getObjectType() {
                return (this.entityManagerFactory != null ? this.entityManagerFactory.getClass() : EntityManagerFactory.class);
        }

        @Override
        public boolean isSingleton() {
                return true;
        }


        /**
         * Close the EntityManagerFactory on bean factory shutdown.
         */
        @Override
        public void destroy() {
                if (this.entityManagerFactory != null) {
                        if (logger.isInfoEnabled()) {
                                logger.info("Closing JPA EntityManagerFactory for persistence unit '" + getPersistenceUnitName() + "'");
                        }
                        this.entityManagerFactory.close();
                }
        }


        //---------------------------------------------------------------------
        // Serialization support
        //---------------------------------------------------------------------

        private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException {
                throw new NotSerializableException("An EntityManagerFactoryBean itself is not deserializable - " +
                                "just a SerializedEntityManagerFactoryBeanReference is");
        }

        protected Object writeReplace() throws ObjectStreamException {
                if (this.beanFactory != null && this.beanName != null) {
                        return new SerializedEntityManagerFactoryBeanReference(this.beanFactory, this.beanName);
                }
                else {
                        throw new NotSerializableException("EntityManagerFactoryBean does not run within a BeanFactory");
                }
        }


        /**
         * Minimal bean reference to the surrounding AbstractEntityManagerFactoryBean.
         * Resolved to the actual AbstractEntityManagerFactoryBean instance on deserialization.
         */
        @SuppressWarnings("serial")
        private static class SerializedEntityManagerFactoryBeanReference implements Serializable {

                private final BeanFactory beanFactory;

                private final String lookupName;

                public SerializedEntityManagerFactoryBeanReference(BeanFactory beanFactory, String beanName) {
                        this.beanFactory = beanFactory;
                        this.lookupName = BeanFactory.FACTORY_BEAN_PREFIX + beanName;
                }

                private Object readResolve() {
                        return this.beanFactory.getBean(this.lookupName, AbstractEntityManagerFactoryBean.class);
                }
        }


        /**
         * Dynamic proxy invocation handler for an {@link EntityManagerFactory}, returning a
         * proxy {@link EntityManager} (if necessary) from {@code createEntityManager} methods.
         */
        @SuppressWarnings("serial")
        private static class ManagedEntityManagerFactoryInvocationHandler implements InvocationHandler, Serializable {

                private final AbstractEntityManagerFactoryBean entityManagerFactoryBean;

                public ManagedEntityManagerFactoryInvocationHandler(AbstractEntityManagerFactoryBean emfb) {
                        this.entityManagerFactoryBean = emfb;
                }

                @Override
                public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        try {
                                if (method.getName().equals("equals")) {
                                        // Only consider equal when proxies are identical.
                                        return (proxy == args[0]);
                                }
                                else if (method.getName().equals("hashCode")) {
                                        // Use hashCode of EntityManagerFactory proxy.
                                        return System.identityHashCode(proxy);
                                }
                                else if (method.getName().equals("unwrap")) {
                                        // Handle JPA 2.1 unwrap method - could be a proxy match.
                                        Class<?> targetClass = (Class<?>) args[0];
                                        if (targetClass == null) {
                                                return this.entityManagerFactoryBean.getNativeEntityManagerFactory();
                                        }
                                        else if (targetClass.isInstance(proxy)) {
                                                return proxy;
                                        }
                                }
                                return this.entityManagerFactoryBean.invokeProxyMethod(method, args);
                        }
                        catch (InvocationTargetException ex) {
                                throw ex.getTargetException();
                        }
                }
        }

}