java - Persistance.xml vs DispatcherServlet -

i using jpa 2.0, hibernate 3 annotation version, problem confusing in persistence.xml & dispatcherservlet

my persistence.xml file contains:

<?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> 

in dispatcher servlet file have following beans:

<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" /> 

question is: why need put properties (driverclassname, url, username, password) in both persistence.xml , in datasource bean in dispatcherservlet?

i learning , confusing me, please help.

actually have double configuration here.

you need either persistence.xml or bean definitions.

take here