Spring Boot Hello World

Tags:

Creating Hello World

Creating a Gradle Project

$ mkdir spring-boot-hello-world
$ cd spring-boot-hello-world
$ gradle init

Create the Java source directory.

$ mkdir -p src/main/java/sample/springboot

Writing the Source Code

buildscript {
    repositories { mavenCentral() }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:1.5.6.RELEASE")
    }
}

apply plugin: 'java'
apply plugin: 'org.springframework.boot'

repositories { mavenCentral() }
dependencies {
    compile("org.springframework.boot:spring-boot-starter-web")
}
jar.baseName = 'spring-boot-hello-world'

@SpringBootApplication
public class Main {
    public static void main(String[] args) {
        try (ConfigurableApplicationContext ctx = SpringApplication.run(Main.class, args)) {
            Main m = ctx.getBean(Main.class);
            m.hello();
        }
    }

    public void hello() {
        System.out.println("Hello Spring Boot!!");
    }
}

Running the Application

Run with Gradle:

$ gradle bootRun

Or build and run the JAR:

$ gradle build
$ java -jar build/libs/spring-boot-hello-world.jar

Both methods print:

Hello Spring Boot!!

Explanation

The Spring Boot Gradle plugin provides the bootRun task and executable JAR packaging. SpringApplication.run() starts Spring Boot.

@SpringBootApplication combines:

  • @Configuration: Java-based Spring configuration.
  • @EnableAutoConfiguration: Automatic Spring configuration based on dependencies.
  • @ComponentScan: Automatic Bean registration by scanning packages for components.

The second argument to run() passes command-line arguments.

Source Code