hibernate 自动建表为什么没反应？

<bean id="sessionFactory"
        class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean">
        <property name="dataSource">
            <ref bean="dataSource" />
        </property>
        <property name="annotatedClasses">
            <list>        
             <value>pojo.test</value>
            </list>
        </property>
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.dialect">org.hibernate.dialect.MySQLDialect</prop>
                <prop key="hibernate.show_sql">true</prop>
                <prop key="hibernate.dynamic-update">true</prop>
                <prop key="hibernate.hbm2ddl.auto">update</prop> 
                </props>
        </property>
    </bean>

为什么没反应？ 求解！