I believe a short and concise example is worth more then theoretical divagation. Therefore I'll strive to be brief!
Prerequisites
* A subset of these Spring libraries: spring-core, spring-aop, spring-beans, spring-txObtainable from the Spring's homepage
* Java 1.5
Main
Let's go directly to the code:import org.springframework.beans.factory.annotation.Autowired; import org.springframework.context.annotation.AnnotationConfigApplicationContext; import org.springframework.stereotype.Service; @Service public class Main { @Autowired private Runnable proxy; public void run(){ proxy.run(); } public static void main(String[] args) { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext("the.package.to.be.scanned"); ((Main) context.getBean(Main.class)).run(); } }
Now, the most important line for us is "new AnnotationConfigApplicationContext("the.package.to.be.scanned"). It says:
Check every class in the package "the.package.to.be.scanned" and look for those which are annotated by @Service, @Component, @Controller or @Repository and register them as beans. Once it's done, instantiate all the not-lazy singletons and autowire any dependencies needed.
Of course, registered but not instantiated beans may be instantiated later. Note, that by default beans are not-lazy singletons.
DummyThread
Up there you could see that we autowired an instance of a class implementing the Runnable interface (it's not a good idea in a production code; we do it for the sake of simplicity here!)import org.springframework.stereotype.Service; @Service public class DummyThread implements Runnable{ public void run() { System.out.println("run()"); } }
And yes, you should expect "run()" on the conosle as a result of this simple app!
AFactory
Now, you may ask what if I want to register a factory? Is it possible using annotations only? Well... it is!@Service public class ConfWithProfiling extends AFactory{ @Bean(name="proxy", autowire=Autowire.BY_NAME) public Runnable proxy(){ return new DummyThread(); } }
The magic is done by @Bean annotation, it says:
This method knows how to create a bean named "proxy".
Note also the @Service annotation. We need that for our scanner in Main class. Without it, Spring context wouldn't register AFactory class and therefore, the "proxy" bean.
