Having more than one data source

I haven't found a question on this topic so I'll ask. I've never actually tackled something which uses more than one data source. 开发者_如何学PythonOne example would be ETL which requires two data sources. How could such an application be designed?

---

Two data sources, two separate names. Inject each one by their respective bean IDs.

<bean id="fromDataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
    <property name="driverClassName" value="${from.jdbc.driverClassName}"/>
    <property name="url" value="${from.jdbc.url}"/>
    <property name="username" value="${from.jdbc.username}"/>
    <property name="password" value="${from.jdbc.password}"/>
</bean>

<context:property-placeholder location="from.jdbc.properties"/>

<bean id="toDataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
    <property name="driverClassName" value="${to.jdbc.driverClassName}"/>
    <property name="url" value="${to.jdbc.url}"/>
    <property name="username" value="${to.jdbc.username}"/>
    <property name="password" value="${to.jdbc.password}"/>
</bean>

<context:property-placeholder location="to.jdbc.properties"/>

You'd want to have a single DAO, but two instances of it - each with their own data source. One would SELECT from the source, the other would INSERT into the target.

A better way might be to forego Spring and just use bulk transfer mechanisms built into the databases.