Question

我使用Spring MVC 3开发了一个Hibernate项目，并使用Maven 3构建。我使用JPA特别是Hibernate Framework管理持久性;我想配置OpenJpa的现有源代码并不是那么困难，但我是新手，我想知道将项目配置为从Hibernate到OpenJpa的一致方式的步骤是什么。 / p>

问候

Answer 1

按照以下步骤操作：

要切换到注释，您需要：

Add hibernate-annotations and JPA jars
Annotate your classes
Modify hibernate.cfg.xml to use classes instead of mapping files
Modify your HibernateUtil class to use a different configuration (this is the step that tripped me up)

要添加正确的jar，我正在使用Maven并添加了以下附加依赖项：

<dependency>

  <groupId>javax.persistence</groupId>

  <artifactId>persistence-api</artifactId>

  <version>1.0</version>

</dependency>

<dependency>

 <groupId>org.hibernate</groupId>

  <artifactId>hibernate-annotations</artifactId>

  <version>3.3.1.GA</version>

</dependency>

JPA注释有很多优秀的资源，所以我不打算详细讨论。你会看到这样的东西：

@Entity

@Table(name = “USERS”)

public class User {

@Id @GeneratedValue

@Column(name = “USER_ID”)

private Long id;

@Column(name = “FIRST_NAME”)

private String firstName;

@Column(name = “LAST_NAME”)

private String lastName;

@Column(name = “EMAIL”)

private String email;

// etc

}

要更新hibernate.cfg.xml文件，您需要更改以下行：

<mapping resource="org/terracotta/reference/exam/domain/User.hbm.xml"/>

这样的事情：

<mapping class="org.terracotta.reference.exam.domain.User">

如果你做了所有这些并停在那里，你可能会看到这样的例外：

Exception in thread "main" java.lang.ExceptionInInitializerError
    at org.terracotta.reference.exam.domain.HibernateUtil.<clinit>(HibernateUtil.java:15)
    at org.terracotta.reference.exam.domain.Main.main(Main.java:12)
Caused by: org.hibernate.MappingException: An AnnotationConfiguration instance is required to use <mapping class="org.terracotta.reference.exam.domain.User"/>
    at org.hibernate.cfg.Configuration.parseMappingElement(Configuration.java:1600)
    at org.hibernate.cfg.Configuration.parseSessionFactory(Configuration.java:1555)
    at org.hibernate.cfg.Configuration.doConfigure(Configuration.java:1534)
    at org.hibernate.cfg.Configuration.doConfigure(Configuration.java:1508)
    at org.hibernate.cfg.Configuration.configure(Configuration.java:1428)
    at org.hibernate.cfg.Configuration.configure(Configuration.java:1414)
    at org.terracotta.reference.exam.domain.HibernateUtil.<clinit>(HibernateUtil.java:13)

而且，和我一样，你会感到困惑。事实证明，在使用注释时，您需要使用AnnotationConfiguration，它是Configuration的子类，特定于注释。所以，你的HibernateUtil可能看起来像这样：

package org.terracotta.reference.exam.domain;

import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;

public class HibernateUtil {

private static SessionFactory sessionFactory;

static {

try {

sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();

} catch(Throwable t) {

throw new ExceptionInInitializerError(t);

}

}

public static SessionFactory getSessionFactory() {

return sessionFactory;

}

public static void shutdown() 
{

getSessionFactory().close();

}

}

希望有所帮助!!

如何从Hibernate切换到OpenJpa

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