指定这个方法做什么?在声明式事物处理时可以指定一下:
    <bean id="transactionProxy" lazy-init="true"
          class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean" abstract="true">
        <property name="transactionManager">
            <ref bean="transactionManager"/>
        </property>
        <property name="transactionAttributes">
            <props>
                <prop key="save*">PROPAGATION_REQUIRED</prop>
                <prop key="*">PROPAGATION_REQUIRED</prop>
            </props>
        </property>
    </bean>