As part of my New Book, New Directions agenda, I just started diving into Spring. The first interesting discovery was the use of the configuration files to map beans to various persistence layers. Say if I wanted a user object for the session. I would declare a user interface IUser.java and then specify the mapping to a persistence layer using the configuration files.

In the configuration (soundbuilder-servlet.xml file for my main controller, I add a reference to the user bean.

    <bean id="soundBuilderController"
          class="com.owlmountain.soundbuilder.web.SoundBuilderController">
      <property name="methodNameResolver">
        <ref local="mainMethodNameResolver"/>
      </property>
      <property name="daoUser"><ref bean="daoUser"/></property>
       ...
    </bean>
    

In application context configuration file (applicationContext.xml, I define the persistence handler for the user interface. Say I want to use the nifty HSQL DB in-memory database that comes with Spring. I just write the persistence into a class called DaoUserHsql, and enter the mapping to the name "daoUser" in the file.

    
      <bean id="daoUser" 
          class="com.owlmountain.soundbuilder.dao.DaoUserHsql"/>
    
    

Pretty slick, now when I implement my business logic, I'm dealing with interfaces only.