Introducing Spring Framework

Chapter 1 ■ Your First Spring Application
Figure 1-3 shows the result of running the HelloWorldController.java file. Spring Boot will know what to do to
create a web context and response to any request based on the annotation provided. But why am I showing this? Well
if you know how to create a Java web application, you can see that Spring Boot simplifies everything because you’re
not writing any configuration files for a Java web application; it’s configuration free!
Spring Boot, à la Groovy
Spring Boot also provides a powerful interaction with the Groovy programming language, making it even easier to
create applications. But wait! Groovy? What is Groovy? The Groovy programming language is based on Java and of
course is run on the JVM. If you know Java, you already know Groovy. Groovy is a dynamic programming language
that gets rid of all of the boilerplate of any Java class and adds extensible methods to existing Java classes, making it a
powerful language.
I am not going into the details of the Groovy language here, but I will say that it is one of the languages in the JVM
community that has gathered many followers and developers. So the Spring Team has made the interaction between
Groovy and the Spring Framework possible.
Let’s continue with the next example. You are going to create only one file; there is no need to create any structure
as before. Only one file:
• app.groovy
Listing 1-7 shows the app.groovy file.
Listing 1-7. app.groovy
@Controller
class MyApp {
}
@RequestMapping("/")
@ResponseBody
String message() {
return "Hello World!"
}
But why is Listing 1-7 different from Java? I just said that “if you know Java, you know Groovy.” Well, if you add the
public keywords to the class and the method, and you put a semicolon after every statement, you have a Java class.
Note that you are still using some annotations like @controller, @RequestMapping, and @responseBody, similar to
Listing 1-6. But now you are not using any imports! That’s right! There is no package and there are no imports. Spring
Boot will recognize all the annotations used and it will integrate all the libraries in this simple application.
Let’s run the code in Listing 1-7, but before you do so, you need to install Spring Boot (see Appendix A for details
on how to install Spring Boot on your system). Another difference from the previous example (Listing 1-6) is that you
are not using Gradle this time. You are going to use the Spring Boot runtime environment, a command-line tool that
will help you to build and run Groovy examples.
Once you have installed Spring Boot, you can execute the following command:
spring run app.groovy
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