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Java example source code file (JpaPersistService.java)

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

Learn more about this Java project at its project page.

Java - Java tags/keywords

annotation, documented, entitymanager, entitymanagerfactory, entitymanagerfactoryprovider, inject, jpapersistservice, map, nullable, persistence, singleton, string, threadlocal, unitofwork, util, work

The JpaPersistService.java Java example source code

/**
 * Copyright (C) 2010 Google, Inc.
 *
 * 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.google.inject.persist.jpa;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
import com.google.inject.Inject;
import com.google.inject.Provider;
import com.google.inject.Singleton;
import com.google.inject.persist.PersistService;
import com.google.inject.persist.UnitOfWork;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.util.Map;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

/**
 * @author Dhanji R. Prasanna (dhanji@gmail.com)
 */
@Singleton
class JpaPersistService implements Provider<EntityManager>, UnitOfWork, PersistService {
  private final ThreadLocal<EntityManager> entityManager = new ThreadLocal();

  private final String persistenceUnitName;
  private final Map<?,?> persistenceProperties;

  @Inject
  public JpaPersistService(@Jpa String persistenceUnitName,
      @Nullable @Jpa Map<?,?> persistenceProperties) {
    this.persistenceUnitName = persistenceUnitName;
    this.persistenceProperties = persistenceProperties;
  }

  public EntityManager get() {
    if (!isWorking()) {
      begin();
    }

    EntityManager em = entityManager.get();
    Preconditions.checkState(null != em, "Requested EntityManager outside work unit. "
        + "Try calling UnitOfWork.begin() first, or use a PersistFilter if you "
        + "are inside a servlet environment.");

    return em;
  }

  public boolean isWorking() {
    return entityManager.get() != null;
  }

  public void begin() {
    Preconditions.checkState(null == entityManager.get(),
        "Work already begun on this thread. Looks like you have called UnitOfWork.begin() twice"
         + " without a balancing call to end() in between.");

    entityManager.set(emFactory.createEntityManager());
  }

  public void end() {
    EntityManager em = entityManager.get();

    // Let's not penalize users for calling end() multiple times.
    if (null == em) {
      return;
    }

    try {
      em.close();
    }
    finally {
      entityManager.remove();
    }
  }

  private volatile EntityManagerFactory emFactory;

  @VisibleForTesting
  synchronized void start(EntityManagerFactory emFactory) {
    this.emFactory = emFactory;
  }

  public synchronized void start() {
    Preconditions.checkState(null == emFactory, "Persistence service was already initialized.");

    if (null != persistenceProperties) {
      this.emFactory = Persistence
          .createEntityManagerFactory(persistenceUnitName, persistenceProperties);
    } else {
      this.emFactory = Persistence.createEntityManagerFactory(persistenceUnitName);
    }
  }

  public synchronized void stop() {
    Preconditions.checkState(emFactory.isOpen(), "Persistence service was already shut down.");
    emFactory.close();
  }

  @Singleton
  public static class EntityManagerFactoryProvider implements Provider<EntityManagerFactory> {
    private final JpaPersistService emProvider;

    @Inject
    public EntityManagerFactoryProvider(JpaPersistService emProvider) {
      this.emProvider = emProvider;
    }

    public EntityManagerFactory get() {
      assert null != emProvider.emFactory;
      return emProvider.emFactory;
    }
  }
  
  @Documented
  @Retention(RetentionPolicy.RUNTIME)
  @Target(ElementType.PARAMETER)
  private @interface Nullable { }

}

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