Hibernate：如何在Hibernate中配置EntityManager？ [英] Hibernate: How configure EntityManager in Hibernate?

问题描述

我创建了一个hibernate项目，'hibernate工具'由JBoss提供给Eclipse。
生成实体（POJO），然后生成DAO。

这样，例如：

  @Entity 
 @Table（name =area，catalog =project_schema，uniqueConstraints = @UniqueConstraint（columnNames =area））
 public class Area implements java.io.Serializable {
 
 private Integer id; 
私人字符串区域; 
 
 public Area（）{
} 
 
 public Area（String area）{
 this.area = area; 
} 
 
 @Id 
 @GeneratedValue（strategy = IDENTITY）
 @Column（name =id，unique = true，nullable = false）
 public Integer getId（）{
 return this.id; 
} 
 
 public void setId（Integer id）{
 this.id = id; 
} 
 
 @Column（name =area，unique = true，nullable = false，length = 45）
 public String getArea（）{
 return this 。区; 
} 
 
 public void setArea（String area）{
 this.area = area; 
} 
 
} 
  

然后，尊重DAO类（由Hibernate工具生成）：

  @Stateless 
 public class AreaHome {
 
 private static final Log log = LogFactory.getLog（AreaHome.class）; 
 
 @PersistenceContext 
 private EntityManager entityManager; 
 
 public void persist（Area transientInstance）{
 log.debug（persisting Area instance）; 
 try {
 entityManager.persist（transientInstance）; 
 log.debug（persist success）; 
} catch（RuntimeException re）{
 log.error（persist failed，re）; 
 throw re; 
} 
} 
 
 public void remove（Area persistentInstance）{
 log.debug（remove Area instance）; 
 try {
 entityManager.remove（persistentInstance）; 
 log.debug（remove successful）; 
} catch（RuntimeException re）{
 log.error（remove failed，re）; 
 throw re; 
} 
} 
 
 public Area merge（Area detachedInstance）{
 log.debug（merging Area instance）; 
 try {
区域结果= entityManager.merge（detachedInstance）; 
 log.debug（merge success）; 
返回结果; 
} catch（RuntimeException re）{
 log.error（merge failed，re）; 
 throw re; 
} 
} 
 
 public Area findById（Integer id）{
 log.debug（get Area instance with id：+ id）; 
 try {
区域实例= entityManager.find（Area.class，id）; 
 log.debug（get successful）; 
 return instance; 
} catch（RuntimeException re）{
 log.error（get failed，re）; 
 throw re; 
} 
} 
} 
  

但是当我尝试调用 AreaHome.persist（）它启动一个例外'NullPointerException'。

我使用hibernate.cfg.xml配置我的项目，一切都可以正常工作：

 <？xml version = 1.0encoding =UTF-8？> 
<！DOCTYPE hibernate-configuration PUBLIC 
 -  // Hibernate / Hibernate配置DTD 3.0 // EN
http://hibernate.sourceforge.net/hibernate-configuration-3.0 .dtd> 
< hibernate-configuration> 
< session-factory> 
< property name =hibernate.connection.driver_class> com.mysql.jdbc.Driver< / property> 
< property name =hibernate.connection.password>< password>< / property> 
< property name =hibernate.connection.url> jdbc：mysql：//< hostname>：3306 /< schema>< / property> 
< property name =hibernate.connection.username> root< / property> 
<！ - < property name =hibernate.dialect> org.hibernate.dialect.MySQLDialect< / property> - > 
< property name =hibernate.dialect> org.hibernate.dialect.MySQLDialect< / property> 
 
<！ -  SQL  - > 
< property name =hibernate.format_sql> true< / property> 
< property name =hibernate.show_sql> true< / property> 
<！ -  C3P0  - > 
< property name =hibernate.c3p0.acquire_increment> 2< / property> 
< property name =hibernate.c3p0.max_size> 20< / property> 
< property name =hibernate.c3p0.min_size> 5< / property> 
< property name =hibernate.c3p0.timeout> 180< / property> 
< property name =hibernate.c3p0.idle_test_period> 100< / property> 
<！ - 类 - > 
< mapping class =com.suaparte.pojo.Area/> 
< / session-factory> 
< / hibernate-configuration> 
  

当我尝试：

< p $ p> public void persist（Area area）throws ExceptionHandler {
Session session = HibernateUtil.getSessionFactory（）。openSession（）;
try {
session.beginTransaction（）;
session.save（area）;
session.getTransaction（）。commit（）;
} catch（HibernateException他）{
session.getTransaction（）。rollback（）;

抛出新的ExceptionHandler（he.getCause（））;
} finally {
if（session！= null）{
session.close（）;
}
}

}


但是想要使用Hibernate工具生成的DAO，因为它们有EntityManager（应该被注入，但不明显）。

我要做什么？任何想法 ？
对不起，长期的问题，但我想非常清楚我的问题。

解决方案

其实你需要实现EntityManagerFactory。

创建驻留在META-INF文件夹中的persistence.xml文件。

看一下例子

http://docs.jboss.org/hibernate/entitymanager/3.6/reference/en/html_single/#setup-configuration-packaging

命令创建EntityManagerFactory和EntityManager之后，

然后：

  EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory（ JavaStackOver）; 
 EntityManager entityManager = entityManagerFactory.createEntityManager（）; 
  

解决依赖关系，我使用maven：

 <依赖性> 
< groupId> org.hibernate< / groupId> 
< artifactId> hibernate-core< / artifactId> 
< version> 4.0.1.Final< / version> 
< / dependency> 
<依赖关系> 
< groupId> org.hibernate< / groupId> 
< artifactId> hibernate-entitymanager< / artifactId> 
< version> 4.0.1.Final< / version> 
< / dependency> 
<依赖关系> 
< groupId> org.hibernate< / groupId> 
< artifactId> hibernate-annotations< / artifactId> 
< version> 3.5.6-Final< / version> 
< / dependency> 
  

注入您的Dao JPA和完成！

与EntityManager一起使用的优点是可以更改futuro中的Hibernate。否则可以使用会话。

I create a hibernate project with 'hibernate tools'provide by JBoss to Eclipse. Generated the Entities (POJO's) and then the DAO's.

This way for example:

@Entity
@Table(name = "area", catalog = "project_schema", uniqueConstraints = @UniqueConstraint(columnNames = "area"))
public class Area implements java.io.Serializable {

    private Integer id;
    private String area;

    public Area() {
    }

    public Area(String area) {
        this.area = area;
    }

    @Id
    @GeneratedValue(strategy = IDENTITY)
    @Column(name = "id", unique = true, nullable = false)
    public Integer getId() {
        return this.id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    @Column(name = "area", unique = true, nullable = false, length = 45)
    public String getArea() {
        return this.area;
    }

    public void setArea(String area) {
        this.area = area;
    }

}

And then the respectely DAO class (generated by Hibernate Tools too):

@Stateless
public class AreaHome {

    private static final Log log = LogFactory.getLog(AreaHome.class);

    @PersistenceContext
    private EntityManager entityManager;

    public void persist(Area transientInstance) {
        log.debug("persisting Area instance");
        try {
            entityManager.persist(transientInstance);
            log.debug("persist successful");
        } catch (RuntimeException re) {
            log.error("persist failed", re);
            throw re;
        }
    }

    public void remove(Area persistentInstance) {
        log.debug("removing Area instance");
        try {
            entityManager.remove(persistentInstance);
            log.debug("remove successful");
        } catch (RuntimeException re) {
            log.error("remove failed", re);
            throw re;
        }
    }

    public Area merge(Area detachedInstance) {
        log.debug("merging Area instance");
        try {
            Area result = entityManager.merge(detachedInstance);
            log.debug("merge successful");
            return result;
        } catch (RuntimeException re) {
            log.error("merge failed", re);
            throw re;
        }
    }

    public Area findById(Integer id) {
        log.debug("getting Area instance with id: " + id);
        try {
            Area instance = entityManager.find(Area.class, id);
            log.debug("get successful");
            return instance;
        } catch (RuntimeException re) {
            log.error("get failed", re);
            throw re;
        }
    }
}

But when I try to call AreaHome.persist() it launchs an exception 'NullPointerException'.

I configure my project with hibernate.cfg.xml and everything works fine though:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="hibernate.connection.password"><password></property>
        <property name="hibernate.connection.url">jdbc:mysql://<hostname>:3306/<schema></property>
        <property name="hibernate.connection.username">root</property>
        <!-- <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property> -->
        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>

        <!-- SQL -->
        <property name="hibernate.format_sql">true</property>
        <property name="hibernate.show_sql">true</property>
        <!-- C3P0 -->
        <property name="hibernate.c3p0.acquire_increment">2</property>
        <property name="hibernate.c3p0.max_size">20</property>
        <property name="hibernate.c3p0.min_size">5</property>
        <property name="hibernate.c3p0.timeout">180</property>
        <property name="hibernate.c3p0.idle_test_period">100</property>
        <!-- Classes -->
        <mapping class="com.suaparte.pojo.Area" />
    </session-factory>
</hibernate-configuration>

This works fine when I try:

public void persist(Area area) throws ExceptionHandler {
    Session session = HibernateUtil.getSessionFactory().openSession();
    try {
        session.beginTransaction();
        session.save(area);
        session.getTransaction().commit();
    } catch (HibernateException he) {
        session.getTransaction().rollback();

        throw new ExceptionHandler(he.getCause());
    } finally {
        if (session != null) {
            session.close();
        }
    }

}

But I want to use the DAO's generated by Hibernate Tools because they have EntityManager (which is supposed to be injected, but isn't apparentely).

What I have to do ? Any idea ? Sorry by the long question, but I wanna to be very clear about my problem.

解决方案

In fact you need to implement a EntityManagerFactory.

Create a persistence.xml file that resides in the META-INF folder.

Take a look at example

http://docs.jboss.org/hibernate/entitymanager/3.6/reference/en/html_single/#setup-configuration-packaging

after the commands to create the EntityManagerFactory and EntityManager then:

EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("JavaStackOver");
EntityManager entityManager = entityManagerFactory.createEntityManager();

Resolve dependencies, I used maven:

<dependency>
  <groupId>org.hibernate</groupId>
  <artifactId>hibernate-core</artifactId>
  <version>4.0.1.Final</version>
</dependency>
<dependency>
  <groupId>org.hibernate</groupId>
  <artifactId>hibernate-entitymanager</artifactId>
  <version>4.0.1.Final</version>
</dependency>
<dependency>
  <groupId>org.hibernate</groupId>
  <artifactId>hibernate-annotations</artifactId>
  <version>3.5.6-Final</version>
</dependency>

Inject on your Dao JPA and Done!

The advantage of working with EntityManager is to have the option to change the Hibernate in futuro. Otherwise could use the Session.

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