Introduction to Spring Boot CLI

1. Introduction

Spring Boot CLI is a command-line abstraction that allows us to easily run Spring micro-services expressed as Groovy scripts. It also provides simplified and enhanced dependency management for those services.

This short article takes a quick look at how to configure Spring Boot CLI and execute simple terminal commands to run pre-configured micro-services.

We’ll use Spring Boot CLI 2.0.0.RELEASE for this article. The newest version of Spring Boot CLI can be found over at Maven Central.

2. Setting Up Spring Boot CLI

One of the easiest ways to set up Spring Boot CLI is to use SDKMAN. Setup and installation instructions for SDKMAN can be found here.

After installing SDKMAN, run the following command to automatically install and configure Spring Boot CLI:

$ sdk install springboot

To verify the install, run the command:

$ spring --version

We can also install Spring Boot CLI by compiling from source, and Mac users can use pre-built packages from Homebrew or MacPorts. See the official docs for all installation options.

3. Common Terminal Commands

Spring Boot CLI provides several useful commands and features out-of-the-box. One of the most helpful features is Spring Shell, which wraps commands with the necessary spring prefix.

To start the embedded shell, we run:

spring shell

From here, we can directly enter desired commands without pre-pending the spring keyword (since we’re now in spring shell).

For example, we can display the current version of the running CLI by typing:

version

One of the most important commands is telling Spring Boot CLI to run a Groovy script:

run [SCRIPT_NAME].groovy

Spring Boot CLI will either automatically infer the dependencies or will do so given the correctly supplied annotations. After this, it will launch an embedded web container and app.

Let’s take a closer look at how to use Groovy script with Spring Boot CLI!

4. Essential Groovy Scripts

Groovy and Spring come together with Spring Boot CLI to allow powerful, performant micro-services to be quickly scripted in single-file Groovy deployments.

Support for multiply-scripted applications usually requires additional build tools like Maven or Gradle.

Below we’ll cover some of the most common use-cases for Spring Boot CLI, reserving more complex setups for other articles.

For a list of all Spring-supported Groovy annotations, please check out the official docs.

4.1. @Grab

The @Grab annotation and Groovy’s Java-esque import clauses allow for easy dependency management and injection.

In fact, most annotations abstract, simplify, and automatically include the necessary import statements. This allows us to spend more time thinking about architecture and the underlying logic of the services we want to deploy.

Let’s take a look at how to use the @Grab annotation:

package org.test

@Grab("spring-boot-starter-actuator")

@RestController
class ExampleRestController{
  //...
}

As we can see, spring-boot-starter-actuator comes pre-configured allowing for succinct script deployment without requiring a customized application or environmental properties, XML, or other programmatic configuration, though each of those things can be specified when necessary.

The full list of @Grab arguments — each specifying a library to download and import — is available here.

4.2. @Controller, @RestController, and @EnableWebMvc

To further expedite deployment, we can alternatively utilize Spring Boot CLI’s provided “grab hints” to automatically infer correct dependencies to import.

We’ll go over some of the most common use cases below.

For example, we can use the familiar @Controller and @Service annotations to quickly scaffold a standard MVC controller and service:

@RestController
class Example {
 
    @Autowired
    private MyService myService;

    @GetMapping("/")
    public String helloWorld() {
        return myService.sayWorld();
    }
}

@Service
class MyService {
    public String sayWorld() {
        return "World!";
    }
}

Spring Boot CLI supports all default configuration for Spring Boot. So, we can our Groovy apps will automatically access static resources from their usual default locations.

4.3. @EnableWebSecurity

To add Spring Boot Security options to our app, we can use the @EnableWebSecurity annotation, which will then be automatically downloaded by Spring Boot CLI.

Below, we’ll abstract part of this process using the spring-boot-starter-security dependency, which leverages the @EnableWebSecurity annotation under the hood:

package bael.security

@Grab("spring-boot-starter-security")

@RestController
class SampleController {

    @RequestMapping("/")
    public def example() {
        [message: "Hello World!"]
    }
}

For more details on how to protect resources and handle security, please check out the official documentation.

4.4. @Test

To set up a simple JUnit test, we can add the @Grab(‘junit’) or @Test annotations:

package bael.test

@Grab('junit')
class Test {
    //...
}

This will allow us to execute JUnit tests easily.

4.5. DataSource and JdbcTemplate

Persistent data options can be specified including DataSource or JdbcTemplate without explicitly using the @Grab annotation:

package bael.data

@Grab('h2')
@Configuration
@EnableWebMvc
@ComponentScan('bael.data')
class DataConfig {

    @Bean
    DataSource dataSource() {
        return new EmbeddedDatabaseBuilder()
          .setType(EmbeddedDatabaseType.H2).build();
    }

}

By simply using familiar Spring bean configuration conventions, we’ve grabbed the H2 embedded database and set it as the DataSource.

5. Custom Configuration

There are two primary ways to configure a Spring Boot micro-service using Spring Boot CLI:

1. we can add argument parameters to our terminal commands
2. we can use a customized YAML file to provide an application configuration

Spring Boot will automatically search the /config directory for application.yml or application.properties

├── app
    ├── app.groovy
    ├── config
        ├── application.yml
    ...

We can also set up:

├── app
    ├── example.groovy
    ├── example.yml
    ...

A full list of application properties can be found here at Spring.

6. Conclusion

This concludes our quick walk-through of Spring Boot CLI! For more details, check out the official docs.