So far we have only injected constructor and property values with static values, which is useful if you want to eliminate configuration files. Values can also be injected by reference -- one bean definition can be injected into another. To do this, you use the constructor-arg or property's ref attribute instead of the value attribute. The ref attribute then refers to another bean definition's id.

In the following example, the first bean definition is a java.lang.String with the id springMessage. It is injected into the second bean definition by reference using the property element's ref attribute.

                
<bean id="springMessage" 
      class="java.lang.String">
    <constructor-arg value="Spring comes before summer." />
</bean>

<bean id="message"
      class="org.springbyexample.springindepth.chapter02.referenceSetterInjection.Message">
    <property name="message" ref="springMessage" />
</bean>