Instantiating arbitrary classes thru Spring

Question

I'm writing a service registry class. This service registry will scan packages for annotated classes and then populate some internal map. What I need then, is to be able to query for services (by String name) using some method (let's say Object get(String name) ). This method will then search internal map for a service with such name and returns instance.

What I'm doing right now, is having this ServiceRegistryBean implement ApplicationContextAware and BeanDefinitionRegistryPostProcessor and a list of Strings (package names) given on construct.

Then, as soon as the bean is constructed, registry post processor kicks in (see note) and the registry class adds the service classes as new beans (singleton, lazy loaded) to the spring bean registry. Then, getting the service instance is as simple as requesting a bean from context, returning singleton instance.

My question is: is there a better way in Spring to do this? I've looked into bean factories, but it does not seem to me the same. Support for auto-wiring and DI in service instances is essential, that's why I want Spring to instantiate it. Also, I like the idea of Spring taking care of singletons.

Note: I've found out, that when I inline the bean creation in <constructor-arg> (that is, bean is not named and is just an instance passed as constructor argument of other bean - in my case, I'm passing registry as a parameter to other constructor), BeanDefinitionRegistryPostProcessor interface methods (namely public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) ) is not called at all! I'm quite sure, it is some behavior of Spring I don't know about, but I was not able to find proper documentation for the post-processor.

Thank you for any hints or insights!

Answer 1

Scanning for custom annotations it's already supported, you only need to add a include-filter to <context:component-scan> tag, ie

<context:component-scan base-package="org.example">
   <context:include-filter type="annotation" expression="some.Annotation"/>
</context:component-scan>

see http://static.springsource.org/spring/docs/current/spring-framework-reference/html/beans.html#beans-scanning-filters

If you turn on default-lazy-init I suppose that the DI Container is ready to use as Service Locator Registry.

About the note, only root bean definitions are taken into account when looking for BeanFactoryPostProcessors , inner beans are ignored.

Usually, scanning and registering beans is done by BeanDefinitionParsers instead because you known when the beans are registered and beans are visible for tools, like STS Spring Bean Explorer, but using a BeanDefinitionRegistryPostProcessor is correct. The interface ensures that beans are defined before other BeanFactoryPostProcessors run.