How do I access beans from Spring container if I use @ComponentScan

[Stefan Jankovic]

So far, I have used XML file for component-scan of my entire application. Then, to access bean(s) from Spring Container, I would do something like:

public class Main {

	public static void main(String[] args) {
		ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
		Dog dog = context.getBean("dog", Dog.class);
	}

}

But then I learned that I can have class annotated with @ComponentScan that serves the same purpose.

So, instead of writing this in XML file:

<context:component-scan base-package="com.example"/>

, I can do this instead:

@Configuration
@ComponentScan(basePackages = "com.example")
public class Test {
	...
}

But I am stuck now. How do I access beans from Spring Container now? Because component-scan from XML is replaced with @ComponentScan, meaning I can't anymore do:

ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");

[Stephan van Hulst]

The main method is not the proper place to get beans from the application context. It's only there to set up the application context.

When a request hits your application, Spring will create controllers and inject beans automatically. You just need to annotate your classes with annotations that indicate that those instances are also managed by Spring. Examples include @Component, @Controller, etc.

[Stefan Jankovic]

Yes, I know how to do that. But for the sake of this example, how do I test those beans using main() method?

I am following one book and I would like to do everything from scratch without making actual requests to my app.

[Tim Holloway]

If what you want to do is test beans, use a test framework. Such as Junit.

JUnit is an external testing system. It does not require modifications to application code to use - and modifications can alter the reliability and security of the application, so it's better to avoid them. You don't need a Main() method, because the Main() for JUnit testing is within JUnit itself.

If you're using a build system such as Maven, the build system can run unit testing as part of the build process and in many cases even generate reports. Many of the "big ticket" open-source projects are built and tested by Maven.

[Paul Crane]

Use another implementation of ApplicationContext - AnnotationConfigApplicationContext. So write just like that:

ApplicationContext context = new AnnotationConfigApplicationContext(Test.class); // creating a new context based on the Test configuration class

@ComponentScan means IoC container(your context) finds and creates all the beans itself. So if you annotate your classes as @Component, then your configuration class scans all these annotated classes and creates beans.