OpenEntityManagerWithNoTransactionTransactionTemplate.java

package fr.openwide.core.jpa.more.business.task.transaction;

import org.springframework.transaction.PlatformTransactionManager;
import org.springframework.transaction.TransactionException;
import org.springframework.transaction.support.SimpleTransactionStatus;
import org.springframework.transaction.support.TransactionCallback;
import org.springframework.transaction.support.TransactionTemplate;

import fr.openwide.core.jpa.util.EntityManagerUtils;

/**
 * <p>Fake TransactionTemplate which open entity manager but doesn't open any transaction.</p>
 * For the following usages:
 * <ul>
 * 		<li>read-only task</li>
 * 		<li>long task with inner atomic transactions, to avoid huge database lock</li>
 * </ul>
 */
public class OpenEntityManagerWithNoTransactionTransactionTemplate extends TransactionTemplate {

	private static final long serialVersionUID = 753594542926029239L;

	private EntityManagerUtils entityManagerUtils;

	public OpenEntityManagerWithNoTransactionTransactionTemplate(EntityManagerUtils entityManagerUtils, PlatformTransactionManager transactionManager, boolean readOnly) {
		super(transactionManager);
		this.entityManagerUtils = entityManagerUtils;
		setReadOnly(readOnly);
	}

	@Override
	public <T> T execute(TransactionCallback<T> action) throws TransactionException {
		try {
			entityManagerUtils.openEntityManager();
			// We do not  call super() here, no transaction will be opened.
			// Note : it doesn't exist any transaction manager which doesn't open transaction while
			// keeping entity manager open.
			return action.doInTransaction(new SimpleTransactionStatus());
		} finally {
			entityManagerUtils.closeEntityManager();
		}
	}

}