使用Spring框架写JPA程序

1.不建议使用Spring的Support类。
  虽然Spring提供JpaTemplate类和JpaDaoSupport类，还是建议使用DI的方式注入EntityManager。例子如下：
    @PersistenceContext
    private EntityManager em;
  另外需要在XML里面注册2个bean。
    <bean
        class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor">
    </bean>
    <bean
        class="org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor">
    </bean>
摘录JavaDoc里的相关描述：
NOTE: JpaTemplate mainly exists as a sibling of JdoTemplate and HibernateTemplate, offering the same style for people used to it. For newly started projects, consider adopting the standard JPA style of coding data access objects instead, based on a "shared EntityManager" reference injected via a Spring bean definition or the JPA PersistenceContext annotation. (Using Spring's SharedEntityManagerBean / PersistenceAnnotationBeanPostProcessor, or using a direct JNDI lookup for an EntityManager on a Java EE 5 server.)

2.EntityManagerFactory相关的XML定义
    <bean id="dataSource"
        class="org.apache.commons.dbcp.BasicDataSource">
        <property name="driverClassName"
            value="com.mysql.jdbc.Driver">
        </property>
        <property name="url"
            value="jdbc:mysql://localhost:3306/SpringStudy">
        </property>
        <property name="username" value="root"></property>
        <property name="password" value="pwd"></property>
    </bean>
    <bean id="emf"
        class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
    <property name="dataSource" ref="dataSource"></property>
    <property name="jpaVendorAdapter" ref="jpaVendorAdapter"></property>
    </bean>
    <bean id="jpaVendorAdapter"
        class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
        <property name="database" value="MYSQL"></property>
        <property name="showSql" value="true"></property>
        <property name="generateDdl" value="false"></property>
        <property name="databasePlatform"
            value="org.hibernate.dialect.MySQL5Dialect">
        </property>
    </bean>

3.JpaTransactionManager相关的XML定义，其中会引用到上面定义的EntityManagerFactory。
    <bean id="jpaDialect"
        class="org.springframework.orm.jpa.vendor.HibernateJpaDialect">
    </bean>
    <bean id="transactionManager"
        class="org.springframework.orm.jpa.JpaTransactionManager">
        <property name="entityManagerFactory" ref="emf"></property>
        <property name="jpaDialect" ref="jpaDialect"></property>
    </bean>
   <tx:annotation-driven transaction-manager="transactionManager" />
   通过上面的定义在BeanClass里面通过@Transactional注解就可以引入事物管理功能。

4.基于注解的autowire
    <context:annotation-config></context:annotation-config>
    通过上面的定义就可以实现@Autowired注解标记对象的自动注入。@Autowired是ByType注入。如果需要ByName注入可以使用@Resource注解。使用上面的定义方式被注入的bean还是需要通过XML的方式注册的。如果连bean的注册都希望通过注解的方式完成的话，使用下面的定义方式来替代。
    <context:component-scan base-package="xxx.package.name"></context:component-scan>
    相关package下被@Component，@Service, @Controller，@Repository之中的任何一个注解标记的Class都会被自动注册成Bean。