Retrieving specific configured object instances generically

[virgo_ct]

I want to be able to retrieve transport-specific instances of connection objects to different business servers (call them A, B, ...). Call the transports (such as CORBA) X, Y, ... .

There will be a bean declaration for each business server connection, for each transport type. I thus have bean declarations as follows:

<bean id="XTransportForA" class="XTransport">
		<properties specific to transport X for business server A connection that are set on XTransport...>
	</bean>

<bean id="XTransportForB" class="XTransport">
		<properties specific to transport X for business server B connection that are set on XTransport...>
	</bean>

<bean id="YTransportForA" class="YTransport">
		<properties specific to transport Y for business server A connection that are set on YTransport...>
	</bean>

<bean id="YTransportForB" class="YTransport">
		<properties specific to transport Y for business server B connection that are set on YTransport...>
	</bean>

etc.

Is it possible, for example, to call a generic bean that is transport-independent such as

<bean id="TransportForA" class="Transport"/>

(where XTransport and YTransport extend Transport) and be returned the transport-specific bean XTransportForA if X was the specified transport (from a properties file)? i.e. can Spring return beans conditionally? Or do I need to write a special factory class?

[Alarmnummer]

So in essence: you want to have a bean that is created in the appcontext, based on some input argument?

Object bean = appContext.getBean("transport","X");

[virgo_ct]

Ideally I'd like to pass the business server type in getBean(), but I want Spring to choose the correct bean instance based on this AND a setting for the transport, which Spring reads from a properties file (I want the transport type to be transparent to the code getting the bean). Is this possible?

[manifoldronin]

One way I can think of is:
0. Declare all the transports as you have already done in the OP.
1. Write a BeanFactoryPostProcessor that reads the transport type from a properties file, and registers some transport-type-agnostic aliases for the transports. E.g., if the transport type, "X" or "Y", is read into variable transportType, you'd do:

factory.registerAlias( transportType + "TransportForA", "transportForA");
factory.registerAlias( transportType + "TransportForB", "transportForB");

2. Now the code getting the bean can do:

appContext.getBean("transportFor" + businessType);

Oh well, maybe I have just made it overly complicated...

[virgo_ct]

Interesting suggestion, would probably work, but would be a bit inelegant, when I think Spring should probably have some mechanism to do this properly. I also find it frustrating not being able to pass parameters when getting beans. Because I can't, I have to use a manual factory... correct me if I'm wrong.

[Colin Yates]

Why can't you just have a bean which takes a map of names:transportBeans?

  <bean id="transportRegistry" class="TransportRegistry">
    <constructor-arg index="0">
      <map>
        <entry key="x"><ref bean="transportX"/></entry>
        <entry key="y"><ref bean="transportY"/></entry>
      </map>
    </constructor-arg>
  </bean>

You transportRegistry would then have a "getTransport(final String key)" and return the corresponding transport?

Have I missed something?

[jbetancourt]

Check out this thread: http://forum.springframework.org/showthread.php?t=12180

It discusses the getBean with runtime arguments, which may be of relevance.

[virgo_ct]

yatesco, thanks, I am actually using a PropertyPlaceholderConfigurer with BeanReferenceFactoryBean to retrieve the name of the transport, without a post-processor:

<bean id="busserver1CorbaTransport" class="CorbaTransport">
		<property name="orbFactory"><ref local="orbFactory" /></property>
		<property name="corba_locator_ior" value="$&#123;corba_locator_ior&#125;" />
		<property name="corba_service_name" value="$&#123;corba_service_name&#125;" />
	</bean>
	
	<bean id="busserver1Transport" class="org.springframework.beans.factory.config.BeanReferenceFactoryBean">
		<property name="targetBeanName" value="busserver1$&#123;transport.type&#125;Transport"/>
	</bean>

I then simply get the bean "busserver1Transport", which will resolve to "busserver1CorbaTransport" if transport.type = Corba ;-)

jbetancourt, thanks for the link, I'll check it out. Looks promising.

[dejanp]

Having separate context xml files for different transports (defining public beans under the same name) and then loading only the appropriate one at the startup sounds like a viable solution to me.