PersistenceService.java

/**
 * Copyright (C) 2012 KRM Associates, Inc. healtheme@krminc.com
 *
 * 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 com.krminc.phr.dao;

import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.persistence.EntityManager;
import javax.transaction.UserTransaction;

/**
 * Utility class for dealing with persistence.
 *
 * @author Daniel Shaw (dshaw.com)
 */
public class PersistenceService {
    private static String DEFAULT_PU = "PHRPU";

    private static ThreadLocal<PersistenceService> instance = new ThreadLocal<PersistenceService>() {
        @Override
        protected PersistenceService initialValue() {
            return new PersistenceService();
        }
    };

    private EntityManager em;

    private UserTransaction utx;

    private PersistenceService() {
        try {
            this.em = (EntityManager) new InitialContext().lookup("java:comp/env/persistence/" + DEFAULT_PU);
            this.utx = (UserTransaction) new InitialContext().lookup("java:comp/UserTransaction");
        } catch (NamingException ex) {
            throw new RuntimeException(ex);
        }
    }

    /**
     * Returns an instance of PersistenceService.
     *
     * @return an instance of PersistenceService
     */
    public static PersistenceService getInstance() {
        return instance.get();
    }


    private static void removeInstance() {
        instance.remove();
    }

    /**
     * Returns an instance of EntityManager.
     *
     * @return an instance of EntityManager
     */
    public EntityManager getEntityManager() {
        return em;
    }

    /**
     * Begins a resource transaction.
     */
    public void beginTx() {
        try {
            utx.begin();
            em.joinTransaction();
        } catch (Exception ex) {
            throw new RuntimeException(ex);
        }
    }

    /**
     * Commits a resource transaction.
     */
    public void commitTx() {
        try {
            utx.commit();
        } catch (Exception ex) {
            throw new RuntimeException(ex);
        }
    }

    /**
     * Rolls back a resource transaction.
     */
    public void rollbackTx() {
        try {
            utx.rollback();
        } catch (Exception ex) {
            throw new RuntimeException(ex);
        }
    }

    /**
     * Closes this instance.
     */
    public void close() {
        removeInstance();
    }
}