Good way to access Spring singleton from within domain objects?

Question

I have a domain model that consists of fairly large object graphs, where domain objects are creating other domain objects and so forth. Each of these domain objects needs access to a small handful of singleton-type helper objects for various purposes.

I was about to implement them using the Java singleton pattern when I remembered that I am already using Spring and I can use Spring to instantiate one of each of these helpers at application startup.

My question is how to I find them from within my domain objects? These are all objects that are created via the "new" operator and are not under the control of Spring.

I'm thinking I could use the "getBean" method if I had my hands on the Spring application context (which I don't) -- but is the performance of this good? I need this stuff to be fast... And how to quickly get the application context?

Answer 1

look at the answer to the question @ http://stackoverflow.com/questions/310271/injecting-beans-into-a-class-outside-the-spring-managed-context

Answer 2

In a typical Spring application, the kind of cross-entity logic you're describing is usually implemented in the business service layer (i.e. the Spring-managed singletons), not the domain objects. Domain classes in Spring apps tend to be fairly simple data containers, perhaps with some methods for performing basic operations on the data they encapsulate, but stopping well short of managing complex object graphs outside of themselves. So business service objects manage domain objects, not the other way around.

If you insist on injecting singletons into your domain objects, though, you can achieve this using AspectJ. Spring itself does not support this very well.

Answer 3

public class SpringApplicationContextProvider implements ApplicationContextAware {
  public void setApplicationContext(ApplicationContext ctx)
        throws BeansException {
      // Wiring the ApplicationContext into a static method
      SpringApplicationContext.setApplicationContext(ctx);
  }
}

And define SpringApplicationContext as,

public class SpringApplicationContext {
   private static ApplicationContext ctx;

   public static void setApplicationContext(
        ApplicationContext applicationContext) {
      ctx = applicationContext;
   }


   public static ApplicationContext getApplicationContext() {
      return ctx;
   }

   private SpringApplicationContext(){

   }
}

Define SpringApplicationContextProvider as a spring bean in your config file. Now the application context can be accessed using this provider.