[Springframework-developer] Q: Magic behind PropertyConfigurer

[Alexi P. <apo...@ya...>]

Hi all,

In Petclinic I see following in applicationContext.xml

    <bean id="propertyConfigurer" 
class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property 
name="location"><value>/WEB-INF/jdbc.properties</value></property>
    </bean>

The  location property in PropertyPlaceholderConfigurer is of type 
Resource. The question is, how does Spring "knows" to take 
/WEB-INF/jdbc.properties string and construct an instance wich 
implements a Resource interface. How does it knows what implementation 
of this interface to use?

The second part of my question is a "real question". What I would like 
to do is to have PropertyConfigurer to setup different property set 
based on context (system property).

The reason I need it is for moving code from one environment to another. 
For example when I move my app. from development to production my DB is 
changing so I would like my PropertyConfigurer to read different 
property file based on some system property which identifies environment.

The way I am trying to do it is by creating a special subclass of a 
Resource which uses a ResourceBundle instead of single property file. 
Each locale in ResourceBundle represents an environment (dev, test, 
prod). My context now looks like that:

     <bean id="resourceA" class="myresources.ContextualResource">
    </bean>
       
    <bean id="propertyConfigurer" 
class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="locations">
                    <list>
                        <ref local="resourceA"/>
                    </list>
                </property>
    </bean>

Does it sound like a resonable approach? Has somebody done it before ? 
Is it better way of doing this ?

Thanks, Alexi