PersistenceAnnotationBeanPostProcessor是否可以使用？ [英] Is PersistenceAnnotationBeanPostProcessor of any use at all?

问题描述

根据其JavaDoc，PersistenceAnnotationBeanPostProcessor似乎负责使用注释@PersistenceContext注入EntityManager。它似乎暗示如果没有在Spring应用程序上下文xml中声明这个bean，@ PerersContext注释将不起作用。

According to its JavaDoc, PersistenceAnnotationBeanPostProcessor seems to be responsible for injecting the EntityManager with the annotation @PersistenceContext. It appears to imply without this bean declared in the Spring application context xml, the @PersistenceContext annotation won't work.

然而，根据我的实验，这不是事实。

However, based on my experiments, this is not the truth.

<persistence xmlns="http://java.sun.com/xml/ns/persistence"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/persistence 
        http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"
    version="1.0">
    <persistence-unit name="default" transaction-type="RESOURCE_LOCAL" />
</persistence>

Spring应用程序上下文XML

Spring application context XML

<context:component-scan base-package="com.test.dao" />

<bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
    <property name="dataSource" ref="dataSource"/>
    <property name="persistenceUnitName" value="default"/>
    <property name="jpaVendorAdapter">
        <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
            <property name="showSql" value="true"/>
            <property name="generateDdl" value="true"/>
            <property name="databasePlatform" value="org.hibernate.dialect.DerbyDialect"/>
        </bean>
    </property>
</bean>

<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
    <property name="driverClassName" value="org.apache.derby.jdbc.ClientDriver"/>
    <property name="url" value="jdbc:derby://localhost:1527/c:\derbydb\mydb"/>
    <property name="username" value="APP"/>
    <property name="password" value="APP"/>
</bean>

<tx:annotation-driven/>

<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
    <property name="entityManagerFactory" ref="entityManagerFactory" />
</bean>

<!-- 
    <bean id="persistenceAnnotation" class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor" />
 -->

UserDaoImpl

UserDaoImpl

@Repository("userDao")
public class UserDaoImpl implements UserDao {

    @PersistenceContext
    protected EntityManager entityManager;

    @Transactional
    public void save(User user) {
            entityManager.persist(user);
    }
}

无论是评论还是取消注释persistenceAnnotation bean，结果是一样的。离开bean并没有什么坏处，但是这个bean的用途是什么？

Whether I comment or uncomment the persistenceAnnotation bean, the result is the same. It doesn't hurt to leave the bean around, but what's the use of this bean?

我使用的是Spring 3.0.5。

I am using Spring 3.0.5.

有人会提供一个场景，取出这个bean会导致失败吗？

Could someone provide a scenario where taking out this bean will result in failure?

我也不喜欢创建一个空的持久性单元只是为了愚弄Spring。幸运的是，这个问题已在Spring 3.1.0中得到解决。

Also I am not fond of creating an empty persistence unit just to fool Spring. Luckily this problem has been addressed in Spring 3.1.0.

推荐答案

透明地激活 PersistenceAnnotationBeanPostProcessor < context：component-scan /> 元素。确切地说，它是激活bean的< context：annotation-config /> 元素，但是这个元素又被<透明地激活了。上下文：component-scan /> 。

The PersistenceAnnotationBeanPostProcessor transparently activated by the <context:component-scan /> element. To be precise it's the <context:annotation-config /> element that activates the bean but this element in turn gets transparently activated by <context:component-scan />.

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