Thursday, November 21, 2013

I'm pretty new to the Spring Framework, I've been playing around with it and putting a few samples apps together for the purposes of evaluating Spring MVC for use in an upcoming company project. So far I really like what I see in Spring MVC, seems very easy to use and encourages you to write classes that are very unit test-friendly.
Just as an exercise, I'm writing a main method for one of my sample/test projects. One thing I'm unclear about is the exact differences between BeanFactory and ApplicationContext - which is appropriate to use in which conditions?
I understand that ApplicationContext extends BeanFactory, but if I'm just writing a simple main method, do I need the extra functionality that ApplicationContext provides? And just exactly what kind of extra functionality does ApplicationContext provide?
In addition to answering "which should I use in a main() method", are there any standards or guidelines as far as which implementation I should use in such a scenario? Should my main() method be written to depend on the bean/application configuration to be in XML format - is that a safe assumption, or am I locking the user into something specific?
And does this answer change in a web environment - if any of my classes needed to be aware of Spring, are they more likely to need ApplicationContext?
Thanks for any help. I know a lot of these questions are probably answered in the reference manual, but I'm having a hard time finding a clear breakdown of these two interfaces and the pros/cons of each without reading thru the manual with a fine-tooth comb.
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8 Answers

up vote57down voteaccepted
The spring docs are great on this: 3.8.1. BeanFactory or ApplicationContext?. They have a table with a comparison, I'll post a snippet:
Bean Factory
  • Bean instantiation/wiring
Application Context
  • Bean instantiation/wiring
  • Automatic BeanPostProcessor registration
  • Automatic BeanFactoryPostProcessor registration
  • Convenient MessageSource access (for i18n)
  • ApplicationEvent publication
So if you need any of the points presented on the Application Context side, you should use ApplicationContext.
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Great, thanks, this answers the question perfectly! Not sure how I missed that in the documentation. – matt b Oct 28 '08 at 14:06
1 
BeanFactory is lightweight, but if you're going to be using Spring "for real", you may as well go with the ApplicationContext: there is very little overhead involved if you don't use its fancy features, but they're still available for if/when you do use them. –  MetroidFan2002 Oct 29 '08 at 6:21
To me, the primary difference to choose BeanFactory over ApplicationContext seems to be that ApplicationContext will pre-instantiate all of the beans. From the Spring docs:
Spring sets properties and resolves dependencies as late as possible, when the bean is actually created. This means that a Spring container which has loaded correctly can later generate an exception when you request an object if there is a problem creating that object or one of its dependencies. For example, the bean throws an exception as a result of a missing or invalid property. This potentially delayed visibility of some configuration issues is why ApplicationContext implementations by default pre-instantiate singleton beans. At the cost of some upfront time and memory to create these beans before they are actually needed, you discover configuration issues when the ApplicationContext is created, not later. You can still override this default behavior so that singleton beans will lazy-initialize, rather than be pre-instantiated.
Given this, I initially chose BeanFactory for use in integration/performance tests since I didn't want to load the entire application for testing isolated beans. However -- and somebody correct me if I'm wrong -- BeanFactory doesn't support classpath XML configuration. So BeanFactory and ApplicationContext each provide a crucial feature I wanted, but neither did both.
Near as I can tell, the note in the documentation about overriding default instantiation behavior takes place in the configuration, and it's per-bean, so I can't just set the "lazy-init" attribute in the XML file or I'm stuck maintaining a version of it for test and one for deployment.
What I ended up doing was extending ClassPathXmlApplicationContext to lazily load beans for use in tests like so:
public class LazyLoadingXmlApplicationContext extends ClassPathXmlApplicationContext {

    public LazyLoadingXmlApplicationContext(String[] configLocations) {
        super(configLocations);
    }

    /**
     * Upon loading bean definitions, force beans to be lazy-initialized.
     * @see org.springframework.context.support.AbstractXmlApplicationContext#loadBeanDefinitions(org.springframework.beans.factory.xml.XmlBeanDefinitionReader)
     */

    @Override
    protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException {
        super.loadBeanDefinitions(reader);
        for (String name: reader.getBeanFactory().getBeanDefinitionNames()) {
            AbstractBeanDefinition beanDefinition = (AbstractBeanDefinition) reader.getBeanFactory().getBeanDefinition(name);
            beanDefinition.setLazyInit(true);
        }
    }

}
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1 
I would argue that if your unit tests are loading up your full Spring context, they aren't "unit tests", but integration tests. –  matt b Mar 1 '10 at 12:50
1 
Good point. In my case I actually needed to load beans from the context for performance and integration tests, and wrote "unit tests" out of habit. I've edited my answer accordingly. –  Lyle Mar 2 '10 at 15:11 

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