Question

I’ve learnt that I can provide Spring with a <context:property-placeholder> element, which appears to use a PropertyPlaceholderConfigurer to interpolate variables (i.e. replace tokens like ${foo}) against a properties file.

Is there a way to customize the class that’s used for resolving the tokens? In particular, I’d quite like to use an Apache Commons Config Configuration object to provide the values of the tokens, rather than using a properties file.

Answer 1

Yes, subclass PropertyPlaceholderConfigurer and override the loadProperties method. This method is passed a Properties object which you can fill with values however you wish. Alternatively, you can define an alternative implementation of PropertiesPersister and plug that into a normal PropertyPlaceholderConfigurer.

In Spring 3.1 you can pull values directly from your commons configuration object by creating your own PropertySource implementation, and registering it with the application context, typically by using an ApplicationContextInitializer. This blog post provides a good overview of the process. <context:property-placeholder> in Spring 3.1 will pull values from registered PropertySources as well as from any properties files you specify.