Introducing Spring Framework

Chapter 1 ■ Your First Spring Application
@Configuration
@ComponentScan
public class Application {
@Bean
MessageService helloWorldMessageService() {
return new HelloWorldMessage();
}
public static void main(String[] args) {
ApplicationContext context =
new AnnotationConfigApplicationContext(Application.class);
}
}
MessageService service =
context.getBean(MessageService.class);
System.out.println(service.getMessage());
You must have Gradle installed, because this tool will help you to compile, build, and run all your examples.
The following command will run the example. Also remember that this command should be executed from the root
of the project where the build.gradle file is located.
gradle run -DmainClass=com.apress.isf.spring.Application
Running the above command should output something similar to the following:
isf-book$ gradle run -DmainClass=com.apress.isf.spring.Application
:ch01:compileJava UP-TO-DATE
:ch01:compileGroovy UP-TO-DATE
:ch01:processResources UP-TO-DATE
:ch01:classes UP-TO-DATE
:ch01:run
20:37:08.705 [main] DEBUG o.s.b.f.s.DefaultListableBeanFactory - Returning cached instance of
singleton bean 'helloWorldMessageService'
Hello World
■ ■Note You can also run the gradle command from the project base by just adding the chapter’s folder, like so:
$ gradle :ch01:run –DmainClass=com.apress.isf.spring.Application.
The Spring Framework is based on one simple principle: dependency injection. This is a design pattern that
has been around for several years; it works, based on interface design, by injecting through setters or constructors
all of the dependencies and implementations that have collaboration and interaction among classes. The Spring
Framework creates a container that can handle all of this interaction and collaboration between objects.
This simple example defines an interface. In the main class, you are injecting its implementation by using the
@Bean annotation over the helloWorldMessageService method. This will tell the Spring Framework container that
the HelloWorldMessage class is the implementation and it will be used at some point.
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