/*
 * Copyright 2002-2018 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
 *
 *      http://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.support;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.PersistenceException;

import org.springframework.dao.DataAccessException;
import org.springframework.dao.DataAccessResourceFailureException;
import org.springframework.lang.Nullable;
import org.springframework.orm.jpa.EntityManagerFactoryAccessor;
import org.springframework.orm.jpa.EntityManagerFactoryUtils;
import org.springframework.orm.jpa.EntityManagerHolder;
import org.springframework.transaction.support.TransactionSynchronizationManager;
import org.springframework.ui.ModelMap;
import org.springframework.web.context.request.AsyncWebRequestInterceptor;
import org.springframework.web.context.request.WebRequest;
import org.springframework.web.context.request.async.CallableProcessingInterceptor;
import org.springframework.web.context.request.async.WebAsyncManager;
import org.springframework.web.context.request.async.WebAsyncUtils;

Spring web request interceptor that binds a JPA EntityManager to the
thread for the entire processing of the request. Intended for the "Open
EntityManager in View" pattern, i.e. to allow for lazy loading in
web views despite the original transactions already being completed.
This interceptor makes JPA EntityManagers available via the current thread, which will be autodetected by transaction managers. It is suitable for service layer transactions via JpaTransactionManager or JtaTransactionManager as well as for non-transactional read-only execution. 
In contrast to OpenEntityManagerInViewFilter, this interceptor is set up in a Spring application context and can thus take advantage of bean wiring. 
Author:
Juergen Hoeller
See Also:
OpenEntityManagerInViewFilter
JpaTransactionManager
SharedEntityManagerCreator
TransactionSynchronizationManager
Since:
2.0/**
 * Spring web request interceptor that binds a JPA EntityManager to the
 * thread for the entire processing of the request. Intended for the "Open
 * EntityManager in View" pattern, i.e. to allow for lazy loading in
 * web views despite the original transactions already being completed.
 *
 * <p>This interceptor makes JPA EntityManagers available via the current thread,
 * which will be autodetected by transaction managers. It is suitable for service
 * layer transactions via {@link org.springframework.orm.jpa.JpaTransactionManager}
 * or {@link org.springframework.transaction.jta.JtaTransactionManager} as well
 * as for non-transactional read-only execution.
 *
 * <p>In contrast to {@link OpenEntityManagerInViewFilter}, this interceptor is set
 * up in a Spring application context and can thus take advantage of bean wiring.
 *
 * @author Juergen Hoeller
 * @since 2.0
 * @see OpenEntityManagerInViewFilter
 * @see org.springframework.orm.jpa.JpaTransactionManager
 * @see org.springframework.orm.jpa.SharedEntityManagerCreator
 * @see org.springframework.transaction.support.TransactionSynchronizationManager
 */
public class OpenEntityManagerInViewInterceptor extends EntityManagerFactoryAccessor implements AsyncWebRequestInterceptor {

	
Suffix that gets appended to the EntityManagerFactory toString
representation for the "participate in existing entity manager
handling" request attribute.
See Also:
getParticipateAttributeName/**
	 * Suffix that gets appended to the EntityManagerFactory toString
	 * representation for the "participate in existing entity manager
	 * handling" request attribute.
	 * @see #getParticipateAttributeName
	 */
	public static final String PARTICIPATE_SUFFIX = ".PARTICIPATE";


	@Override
	public void preHandle(WebRequest request) throws DataAccessException {
		String key = getParticipateAttributeName();
		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
		if (asyncManager.hasConcurrentResult() && applyEntityManagerBindingInterceptor(asyncManager, key)) {
			return;
		}

		EntityManagerFactory emf = obtainEntityManagerFactory();
		if (TransactionSynchronizationManager.hasResource(emf)) {
			// Do not modify the EntityManager: just mark the request accordingly.
			Integer count = (Integer) request.getAttribute(key, WebRequest.SCOPE_REQUEST);
			int newCount = (count != null ? count + 1 : 1);
			request.setAttribute(getParticipateAttributeName(), newCount, WebRequest.SCOPE_REQUEST);
		}
		else {
			logger.debug("Opening JPA EntityManager in OpenEntityManagerInViewInterceptor");
			try {
				EntityManager em = createEntityManager();
				EntityManagerHolder emHolder = new EntityManagerHolder(em);
				TransactionSynchronizationManager.bindResource(emf, emHolder);

				AsyncRequestInterceptor interceptor = new AsyncRequestInterceptor(emf, emHolder);
				asyncManager.registerCallableInterceptor(key, interceptor);
				asyncManager.registerDeferredResultInterceptor(key, interceptor);
			}
			catch (PersistenceException ex) {
				throw new DataAccessResourceFailureException("Could not create JPA EntityManager", ex);
			}
		}
	}

	@Override
	public void postHandle(WebRequest request, @Nullable ModelMap model) {
	}

	@Override
	public void afterCompletion(WebRequest request, @Nullable Exception ex) throws DataAccessException {
		if (!decrementParticipateCount(request)) {
			EntityManagerHolder emHolder = (EntityManagerHolder)
					TransactionSynchronizationManager.unbindResource(obtainEntityManagerFactory());
			logger.debug("Closing JPA EntityManager in OpenEntityManagerInViewInterceptor");
			EntityManagerFactoryUtils.closeEntityManager(emHolder.getEntityManager());
		}
	}

	private boolean decrementParticipateCount(WebRequest request) {
		String participateAttributeName = getParticipateAttributeName();
		Integer count = (Integer) request.getAttribute(participateAttributeName, WebRequest.SCOPE_REQUEST);
		if (count == null) {
			return false;
		}
		// Do not modify the Session: just clear the marker.
		if (count > 1) {
			request.setAttribute(participateAttributeName, count - 1, WebRequest.SCOPE_REQUEST);
		}
		else {
			request.removeAttribute(participateAttributeName, WebRequest.SCOPE_REQUEST);
		}
		return true;
	}

	@Override
	public void afterConcurrentHandlingStarted(WebRequest request) {
		if (!decrementParticipateCount(request)) {
			TransactionSynchronizationManager.unbindResource(obtainEntityManagerFactory());
		}
	}

	
Return the name of the request attribute that identifies that a request is
already filtered. Default implementation takes the toString representation
of the EntityManagerFactory instance and appends ".FILTERED".
See Also:
PARTICIPATE_SUFFIX/**
	 * Return the name of the request attribute that identifies that a request is
	 * already filtered. Default implementation takes the toString representation
	 * of the EntityManagerFactory instance and appends ".FILTERED".
	 * @see #PARTICIPATE_SUFFIX
	 */
	protected String getParticipateAttributeName() {
		return obtainEntityManagerFactory().toString() + PARTICIPATE_SUFFIX;
	}


	private boolean applyEntityManagerBindingInterceptor(WebAsyncManager asyncManager, String key) {
		CallableProcessingInterceptor cpi = asyncManager.getCallableInterceptor(key);
		if (cpi == null) {
			return false;
		}
		((AsyncRequestInterceptor) cpi).bindEntityManager();
		return true;
	}

}