如何从休眠状态切换到OpenJpa

Question

我有一个用Spring MVC 3开发并用Maven 3构建的Hibernate项目。我使用特定的Hibernate Framework管理JPA的持久性;我想这不是很难配置我现有的OpenJpa源代码，但我对它很陌生，我想知道什么是配置我的项目以从Hibernate到OpenJpa以一致的方式切换的步骤。

问候

Answer 1

遵循以下步骤：

要切换到注释，你需要：

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) 

加入正确的罐子，我使用Maven和补充以下附加依赖关系：

<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> 

在JPA上有许多优良的资源注释，所以我不打算详细讨论这一点。你得东西，看起来像这样：

@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，你要改线路是这样的：

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

到这样的事情：

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

如果你做了这一切，停在那里，你可能会看到这样的异常：

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，像我一样，你会感到困惑。事实证明，在使用注释时，您需要使用AnnotationConfiguration（特定于注释的配置的子类）。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(); 

} 

} 

希望帮助!!