Re: [Springframework-developer] Re: [Springframework-user] setting bean properties from system properties

[Colin S. <col...@ex...>]

Rod Johnson wrote:

>>Of course, the variant to adding more and more mechanisms to access
>>other objects is to put in some (optional) support for an expresion
>>language inside the bean factory. I've been thinking about this for a
>>while now.
>>    
>>
>+1
>
>  
>
>>So assuming that there is a generic expression language plugin facility,
>>and which expression language to use is denoted by a prefix, a
>>hypothetical OGNL example for your case would be:
>>
>><bean id="myBean" class="org.me.myClass">
>>  <property
>>
>>    
>>
>name="myProp"><expr>ognl:@System@getProperties()['my.property.name']</expr><
>/property>
>  
>
>></bean>
>>
>>And if you expose the current factory into the OGNL context, then you
>>could have expressions such as:
>>
>><bean id="myBean" class="org.me.myClass">
>>  <property
>>
>>    
>>
>name="myProp"><expr>ognl:factory.getBean('another-bean-id').someProperty</ex
>pr></property>
>  
>
>></bean>
>>    
>>
>
>I think it's important that we don't sink under steady feature creep of
>supporting more and more single-scenario solutions. So a more general
>solution would be better.
>
>Another 1.1 feature, perhaps.
>
>  
>
There is of course a tradeoff here, where you want to cover the guy 
using a basic BeanFactory in an Applet or somewhere like that where 
every last byte counts, and get him a minimal set of functionality, but 
for the cases where size is not as much of an issue, there are more 
powerful/general solutions.

In this particular case (getting a system property), I think this will 
be able to be handled by the MethodCallFactoryBean I am writing right 
now, in a slightly more verbose fashion...

  <bean id="sysProps" 
class="org.springframework.beans.factory.config.MethodCallFactoryBean">
    <property 
name="staticMethod"><value>java.lang.System.getProperties</value></property>
  </bean>
  <bean id="mySystemProp" 
class="org.springframework.beans.factory.config.MethodCallFactoryBean">
    <property name="target"><ref local='sysProps'/></property>
    <property name="targetMethod"><value>getProperty</value></property>
    <property name="args">
      <list>
        <value>my.property.name</value>
      </list>
  </bean>

So this would cover people using a base beanfactory, while people 
willing to bring in a real expression processor, would have more concise 
mechanisms...