我正在使用 JPA 2.0，Hibernate 3 Annotation 版本，问题是我在 Persistence.xml 和 DispatcherServlet 中感到困惑
我的 persistence.xml 文件包含：
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0"
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_2_0.xsd">
<persistence-unit name="Hello" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<class>models.student</class>
<properties>
<property name="hibernate.show_sql" value="true" />
<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
<property name="javax.persistence.jdbc.url" value="jdbc:mysql://127.0.0.1:3306/test"/>
<property name="javax.persistence.jdbc.user" value="root" />
<property name="javax.persistence.jdbc.password" value="admin" />
<property name="hibernate.dialect" value="org.hibernate.dialect.MySQLInnoDBDialect"/>
</properties>
</persistence-unit>
</persistence>
在我的调度程序 servlet 文件中，我有以下 Bean：
<bean id="dataSource"
class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/test" />
<property name="username" value="root" />
<property name="password" value="admin" />
</bean>
<bean id="entityManagerFactory"
class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
<property name="persistenceUnitName" value="Hello" />
<property name="dataSource" ref="dataSource" />
<property name="jpaVendorAdapter">
<bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
<property name="databasePlatform" value="org.hibernate.dialect.MySQL5InnoDBDialect" />
<property name="showSql" value="true" />
<property name="generateDdl" value="true" />
</bean>
</property>
</bean>
<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
<property name="entityManagerFactory" ref="entityManagerFactory" />
</bean>
<bean class="org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor" />
问题是：为什么我们需要将所有属性（DriverClassName、URL、用户名、密码）都放在 persistence.xml 和 DispatcherServlet 的 DataSource bean 中？
我正在学习，这让我很困惑，请帮助。