Using Spring in standalone apps

Question

I am learning Spring and I have a question regarding how you use it in standalone applications (and also when using it for making web applications). The examples I have been

Answer 1

It kind of depends on the application you are writing, but you should limit getBean() invocations to minimum, preferably one. You are fetching the first bean directly from the context and put the rest of the logic in the beans themselves. Something along the lines:

Bootstrap boot = context.getBean(Bootstrap.class);
boot.start();

And all the rest of your application logic is taking place within start(). It can create threads, listen for events, etc.

Answer 2

One class (your main class, probably) has to be Spring-aware to create the context. All other classes can continue to be wired together via Spring and do not need to be Context-aware.

Answer 3

You're on the right lines. Your main method will initialise your application context as you've discovered. The trick then is to use that app context to create the entry point to your application. That bean, having been created with spring will have been wired for you..

import org.springframework.beans.factory.BeanFactoryUtils;
import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;


public class ApplicationMain {

    public static void main(String[] args) {

        AbstractApplicationContext ctx = new ClassPathXmlApplicationContext("classpath:/META-INF/spring/applicationContext.xml");

        MyApplication app = BeanFactoryUtils.beanOfType(ctx, MyApplication.class);

        app.init();
    }

}

Answer 4

If you're calling context.getBean() everywhere, you're probably missing the whole point of Spring, which is a dependency injection framework.

In a standalone app, you typically call context.getBean() only once (or at least, very rarely), in order to get a "root" bean. This bean is injected by Spring with other beans, and so on.

In a web app, it all depends on which framework you use. But typically, you register a listener in the web.xml which loads the context for you, and controllers are created and/or injected by Spring.