Hibernate 3.2支持JPA注解，Spring集成JPA是可选的。
下面是Spring集成JPA的一个例子。
实体类MyUser，使用JPA注解实现到数据库表myUser的映射，如下所示：
package org.shirdrn.entity;import java.util.Date;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.Transient;@Entitypublic class MyUser {private Long id;private String userName;private String password;private String gender;private Integer age;private Integer birthYear;private String addr;private String email;@Id@GeneratedValue(strategy = GenerationType.IDENTITY)public Long getId() {return id;}public void setId(Long id) {this.id = id;}@Column(name="userName")public String getUserName() {return userName;}public void setUserName(String userName) {this.userName = userName;}@Column(name="password")public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}@Column(name="gender")public String getGender() {return gender;}public void setGender(String gender) {this.gender = gender;}@Column(name="age")public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}@Column(name="addr")public String getAddr() {return addr;}public void setAddr(String addr) {this.addr = addr;}@Column(name="email")public String getEmail() {return email;}public void setEmail(String email) {this.email = email;}@Transientpublic Integer getBirthYear() {return new Integer(2008-age);}public void setBirthYear(Integer age) {this.birthYear = new Integer(2008-age);}}
其中，birthYear不是数据库中的字段，使用JPA的@Transient注解，在映射的时候，会忽略掉该成员 。
持久层DAO接口如下：
package org.shirdrn.dao;import java.util.List;import org.shirdrn.entity.MyUser;import org.springframework.transaction.annotation.Transactional;@Transactionalpublic interface MyUserDAO {public void createMyUser(MyUser myUser);public void deleteMyUser(MyUser myUser);public void updateMyUser(MyUser myUser);public List queryMyUser(String queryString);public List queryAll();}
这里，使用了JPA注解，声明事务。
DAO实现类，如下所示：
package org.shirdrn.dao.impl;import java.util.List;import org.shirdrn.dao.MyUserDAO;import org.shirdrn.entity.MyUser;import org.springframework.orm.jpa.support.JpaDaoSupport;public class MyUserDAOImpl extends JpaDaoSupport implements MyUserDAO {public void createMyUser(MyUser myUser) {getJpaTemplate().persist(myUser);}public void deleteMyUser(MyUser myUser) {MyUser dbMyUser = getJpaTemplate().find(MyUser.class, myUser.getId());getJpaTemplate().remove(dbMyUser);}public void updateMyUser(MyUser myUser) {MyUser dbMyUser = getJpaTemplate().find(MyUser.class, myUser.getId());if(myUser.getUserName() != null){dbMyUser.setUserName(myUser.getUserName());}if(myUser.getAddr() != null){dbMyUser.setAddr(myUser.getAddr());}getJpaTemplate().merge(dbMyUser);}@SuppressWarnings("unchecked")public List queryMyUser(String queryString) {return (List)getJpaTemplate().find(queryString);}@SuppressWarnings("unchecked")public List queryAll() {return (List)getJpaTemplate().find("from MyUser");}}
因为继承了JpaDaoSupport，索引需要获取一个JpaTemplate来实现访问数据库，在Spring的配置文件 中要注入一个org.springframework.orm.jpa.LocalContainerEntityManagerFacToryBean。
Spring的配置文件applicationContext.xml的内容如下所示：
http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:tx="http://www.springframework.org/schema/tx"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans-2.0.xsdhttp://www.springframework.org/schema/txhttp://www.springframework.org/schema/tx/spring-tx-2.0.xsd">
在META-INF目录下，还要加一个persistence.xml配置文件，如下所示： http://java.sun.com/xml/ns/persistence"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://java.sun.com/xml/ns/persistencehttp://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"version="1.0">org.hibernate.ejb.HibernatePersistenceorg.shirdrn.entity.MyUser
接着，对增删改查操作进行测试，如下所示：
插入记录：
packageorg.shirdrn.test;imporTorg.shirdrn.dao.MyUserDAO;imporTorg.shirdrn.entity.MyUser;imporTorg.springframework.context.ApplicationContext;imporTorg.springframework.context.support.ClassPathXmlApplicationContext;publicclassTestCreateMyUser{publicstaticvoidmain(String[]args){MyUserDAOmyUserDAO=(MyUserDAO)ctx.getBean("myUserDAOImpl");MyUsermyUser=newMyUser();myUser.setUserName("JohnXa");myUser.setPassword("123456");myUser.setGender("男");myUser.setAge(newInteger(25));myUser.setAddr("NewYork");myUser.setEmail("john@hotmail.com");myUserDAO.createMyUser(myUser);}}
删除记录： packageorg.shirdrn.test;imporTorg.shirdrn.dao.MyUserDAO;imporTorg.shirdrn.entity.MyUser;imporTorg.springframework.context.ApplicationContext;imporTorg.springframework.ClassPathXmlApplicationContext;publicclassTestDeleteMyUser{publicstaticvoidmain(String[]args){ApplicationContextctx=newClassPathXml("applicationContext.xml");MyUserDAOmyUserDAO=(MyUserDAO)ctx.getBean("myUserDAOImpl");MyUsermyUser=newMyUser();myUser.setId(newLong(29));myUserDAO.deleteMyUser(myUser);
修改记录：
packageorg.shirdrn.test;imporTorg.shirdrn.dao.MyUserDAO;imporTorg.shirdrn.entity.MyUser;imporTorg.springframework.context.ApplicationContext;imporTorg.springframework.context.ClassPathXmlApplicationContext; publicclassTestUpdateMyUser{ publicstaticvoidmain(String[]args){ ApplicationContextctx=newClassPathXmlApplicationContext("applicationContext.xml"); MyUserDAOmyUserDAO=(MyUserDAO)ctx.getBean("myUserDAOImpl"); MyUsermyUser=newMyUser (); myUser.setId(newLong(28)); myUser.setAddr("北京市"); myUserDAO.updateMyUser(myUser); } }
查询记录： packageorg.shirdrn.test;importjava.util.List;imporTorg.shirdrn.dao.MyUserDAO;imporTorg.shirdrn.entity.MyUser;imporTorg.springframework.context.ApplicationContext;imporTorg.springframework.context.ClassPathXmlApplicationContext;publicclassTestQueryAllMyUser{publicstaticvoidmain(String[]args){ApplicationContextctx=newClassPathXmContext("applicationContext.xml");MyUserDAOmyUserDAO=(MyUserDAO)ctx.getBean("myUserDAOImpl");Listlist=myUserDAO.queryMyUser("fromMyUser");for(MyUseruser:list){System.out.println("ID："+user.getId()+"|姓名："+user.getUserName()+"|密码："+user.getPassword()+"|性别："+user.getGender()+"|年龄："+user.getAge()+"|住址："+user.getAddr()+"|邮箱："+user.getEmail());}}}
心得总结
感觉自己对JPA的理解还是不怎么深刻。
JpaTemplate提供的一些操作的方法，感觉不是很快就能理解的。
似乎使用JpaTemplate没有使用HibernateTemplate方便，尤其是在执行插入、修改、删除记录的时候 。修改和删除记录需要先把数据库中对应的记录加载出来，才能执行修改和删除操作。
查询数据库倒是很容易，因为根本不需要事务，如果没有事务，插入、修改和删除操作就不能实现。
在Spring中使用JPA，感觉代价比较大，使用起来不容易，出错不容易调试。
比较好的地方就是。如果数据库中的表很多，无需编写大量的XML文件去映射，而且只需要从POJO中就 可以非常直观地看到各个表之间的关系。
做事不怕难，自无难人事。
