不在JPA 的 persistence.xml 文件中配置Entity class的解决办法

时间:2021-12-03 00:19:14

在Spring 集成 Hibernate 的JPA方式中,需要在persistence配置文件中定义每一个实体类,这样非常地不方便,2种方法可以解决此问题:

这2种方式都可以实现不用在persistence.xml文件中配置每一个实体类,从而免去每个Entity都要在persistence.xml文件中配置的烦恼,但是这种方式Entity实体类的主键字段注解@ID要放到 getXXX()方法上,否则不认。

方式1:
修改“LocalContainerEntityManagerFactoryBean”的配置,如下:

<bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">

<property name="packagesToScan" value="com.sunitjy.model.entityName" />

<property name="jpaVendorAdapter">

<bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter"/>

</property>

<property name="jpaProperties">

<props>

<prop key="hibernate.connection.driver_class">${jdbc.driverClassName}</prop>

<prop key="hibernate.connection.url">${jdbc.url}</prop>

<prop key="hibernate.connection.username">${jdbc.username}</prop>

<prop key="hibernate.connection.password">${jdbc.password}</prop>

<prop key="hibernate.c3p0.min_size">10</prop>

<prop key="hibernate.hbm2ddl.auto">true</prop>

<prop key="hibernate.dialect">${hibernate.dialect}</prop>

</props>

</property>

</bean>

方式1没有使用 persistence 这个配置文件,注意咯!

方式2:
修改“LocalContainerEntityManagerFactoryBean”的配置,如下:

<bean id="entityManagerFactory"
  class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
<!--  <property name="persistenceUnitName" value="pro_persistence"></property>-->
  <property name="dataSource" ref="dataSource"></property>
  <property name="persistenceXmlLocation" value="classpath*:pro_core/jpa_persistence.xml"></property>
  <property name="packagesToScan">
   <list>
    <value>com.paic.lfex.model</value>
    <value>com.lfex.sdp.core.model</value>
    <value>com.paic.lfex.core.pro</value>
   </list>
  </property>
  <property name="jpaVendorAdapter">
   <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter" />
  </property>
 </bean>

persistence.xml配置文件内容:

<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/persistencehttp://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"
 version="1.0">
 <persistence-unit name="pro_persistence"
  transaction-type="RESOURCE_LOCAL">
  <provider>org.hibernate.ejb.HibernatePersistence</provider>
   <properties>
   <property name="hibernate.dialect" value="org.hibernate.dialect.Oracle10gDialect" />
   <property name="current_session_context_class" value="thread" />
   <!--<property name="hibernate.hbm2ddl.auto" value="update" /> -->
   <!--<property name="hibernate.show_sql" value="true" />-->
   <!--<property name="hibernate.format_sql" value="true" />-->
  </properties>

</persistence-unit>

</persistence>

方式2使用了 persistence 配置文件,去掉“persistenceUnitName”属性,添加“packagesToScan”属性,persistence.xml配置文件中的persistence-unit名字照样保留,但是 persistence 配置文件中不需要对实体类进行配置,会自动识别。

为什么去掉“persistenceUnitName”属性就可以自动识别实体了呢?看一下Spring的源码就知道了:

类名:org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager

代码段:

private List<SpringPersistenceUnitInfo> readPersistenceUnitInfos() {

List<SpringPersistenceUnitInfo> infos = new LinkedList<SpringPersistenceUnitInfo>();

boolean buildDefaultUnit = (this.packagesToScan != null || this.mappingResources != null);

PersistenceUnitReader reader = new PersistenceUnitReader(this.resourcePatternResolver, this.dataSourceLookup);

SpringPersistenceUnitInfo[] readInfos = reader.readPersistenceUnitInfos(this.persistenceXmlLocations);

for (SpringPersistenceUnitInfo readInfo : readInfos) {

infos.add(readInfo);

if (this.defaultPersistenceUnitName != null &&

this.defaultPersistenceUnitName.equals(readInfo.getPersistenceUnitName())) {

buildDefaultUnit = false;

}

}

if (buildDefaultUnit) {

infos.add(buildDefaultPersistenceUnitInfo());

}

return infos;

}

注意看这个源码的方法,defaultPersistenceUnitName 变量如果不为空,并且等于 persistence 配置文件中的持久化单元名称,则buildDefaultUnit就为false,buildDefaultUnit 如果为 false,是不会执行 buildDefaultPersistenceUnitInfo() 方法的,而 buildDefaultPersistenceUnitInfo() 方法是根据我们定义的 packagesToScan 去自动扫描Entity实体类的。  

注:我使用的是 Spring 3.2.3

以上2种方法都测试通过。