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.

                
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans 
                           http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="springMessage" 
          class="java.lang.String">
        <constructor-arg value="Spring is fun." />
    </bean>

    <bean id="message"
          class="org.springbyexample.di.xml.SetterMessage">
        <property name="message" ref="springMessage" />
    </bean>

</beans>