The Spring Boot CLI is a command line tool that you can use if you want to quickly develop a Spring application. It lets you run Groovy scripts, which means that you have a familiar Java-like syntax without so much boilerplate code. You can also bootstrap a new project or write your own command for it.

1. Installing the CLI

The Spring Boot CLI (Command-Line Interface) can be installed manually by using SDKMAN! (the SDK Manager) or by using Homebrew or MacPorts if you are an OSX user. See getting-started.html in the “Getting started” section for comprehensive installation instructions.

2. Using the CLI

Once you have installed the CLI, you can run it by typing spring and pressing Enter at the command line. If you run spring without any arguments, a simple help screen is displayed, as follows:

$ spring
usage: spring [--help] [--version]
       <command> [<args>]

Available commands are:

  run [options] <files> [--] [args]
    Run a spring groovy script

  ... more command help is shown here

You can type spring help to get more details about any of the supported commands, as shown in the following example:

$ spring help run
spring run - Run a spring groovy script

usage: spring run [options] <files> [--] [args]

Option                     Description
------                     -----------
--autoconfigure [Boolean]  Add autoconfigure compiler
                             transformations (default: true)
--classpath, -cp           Additional classpath entries
--no-guess-dependencies    Do not attempt to guess dependencies
--no-guess-imports         Do not attempt to guess imports
-q, --quiet                Quiet logging
-v, --verbose              Verbose logging of dependency
                             resolution
--watch                    Watch the specified file for changes

The version command provides a quick way to check which version of Spring Boot you are using, as follows:

$ spring version
Spring CLI v2.2.1.RELEASE

2.1. Running Applications with the CLI

You can compile and run Groovy source code by using the run command. The Spring Boot CLI is completely self-contained, so you do not need any external Groovy installation.

The following example shows a “hello world” web application written in Groovy:

hello.groovy
@RestController
class WebApplication {

    @RequestMapping("/")
    String home() {
        "Hello World!"
    }

}

To compile and run the application, type the following command:

$ spring run hello.groovy

To pass command-line arguments to the application, use -- to separate the commands from the “spring” command arguments, as shown in the following example:

$ spring run hello.groovy -- --server.port=9000

To set JVM command line arguments, you can use the JAVA_OPTS environment variable, as shown in the following example:

$ JAVA_OPTS=-Xmx1024m spring run hello.groovy
When setting JAVA_OPTS on Microsoft Windows, make sure to quote the entire instruction, such as set "JAVA_OPTS=-Xms256m -Xmx2048m". Doing so ensures the values are properly passed to the process.

2.1.1. Deduced “grab” Dependencies

Standard Groovy includes a @Grab annotation, which lets you declare dependencies on third-party libraries. This useful technique lets Groovy download jars in the same way as Maven or Gradle would but without requiring you to use a build tool.

Spring Boot extends this technique further and tries to deduce which libraries to “grab” based on your code. For example, since the WebApplication code shown previously uses @RestController annotations, Spring Boot grabs "Tomcat" and "Spring MVC".

The following items are used as “grab hints”:

Items Grabs

JdbcTemplate, NamedParameterJdbcTemplate, DataSource

JDBC Application.

@EnableJms

JMS Application.

@EnableCaching

Caching abstraction.

@Test

JUnit.

@EnableRabbit

RabbitMQ.

extends Specification

Spock test.

@EnableBatchProcessing

Spring Batch.

@MessageEndpoint @EnableIntegration

Spring Integration.

@Controller @RestController @EnableWebMvc

Spring MVC + Embedded Tomcat.

@EnableWebSecurity

Spring Security.

@EnableTransactionManagement

Spring Transaction Management.
See subclasses of CompilerAutoConfiguration in the Spring Boot CLI source code to understand exactly how customizations are applied.

2.1.2. Deduced “grab” Coordinates

Spring Boot extends Groovy’s standard @Grab support by letting you specify a dependency without a group or version (for example, @Grab('freemarker')). Doing so consults Spring Boot’s default dependency metadata to deduce the artifact’s group and version.

The default metadata is tied to the version of the CLI that you use. It changes only when you move to a new version of the CLI, putting you in control of when the versions of your dependencies may change. A table showing the dependencies and their versions that are included in the default metadata can be found in the appendix.

2.1.3. Default Import Statements

To help reduce the size of your Groovy code, several import statements are automatically included. Notice how the preceding example refers to @Component, @RestController, and @RequestMapping without needing to use fully-qualified names or import statements.

Many Spring annotations work without using import statements. Try running your application to see what fails before adding imports.

2.1.4. Automatic Main Method

Unlike the equivalent Java application, you do not need to include a public static void main(String[] args) method with your Groovy scripts. A SpringApplication is automatically created, with your compiled code acting as the source.

2.1.5. Custom Dependency Management

By default, the CLI uses the dependency management declared in spring-boot-dependencies when resolving @Grab dependencies. Additional dependency management, which overrides the default dependency management, can be configured by using the @DependencyManagementBom annotation. The annotation’s value should specify the coordinates (groupId:artifactId:version) of one or more Maven BOMs.

For example, consider the following declaration:

@DependencyManagementBom("com.example.custom-bom:1.0.0")

The preceding declaration picks up custom-bom-1.0.0.pom in a Maven repository under com/example/custom-versions/1.0.0/.

When you specify multiple BOMs, they are applied in the order in which you declare them, as shown in the following example:

@DependencyManagementBom(["com.example.custom-bom:1.0.0",
        "com.example.another-bom:1.0.0"])

The preceding example indicates that the dependency management in another-bom overrides the dependency management in custom-bom.

You can use @DependencyManagementBom anywhere that you can use @Grab. However, to ensure consistent ordering of the dependency management, you can use @DependencyManagementBom at most once in your application.

2.2. Applications with Multiple Source Files

You can use “shell globbing” with all commands that accept file input. Doing so lets you use multiple files from a single directory, as shown in the following example:

$ spring run *.groovy

2.3. Packaging Your Application

You can use the jar command to package your application into a self-contained executable jar file, as shown in the following example:

$ spring jar my-app.jar *.groovy

The resulting jar contains the classes produced by compiling the application and all of the application’s dependencies so that it can then be run by using java -jar. The jar file also contains entries from the application’s classpath. You can add and remove explicit paths to the jar by using --include and --exclude. Both are comma-separated, and both accept prefixes, in the form of “+” and “-”, to signify that they should be removed from the defaults. The default includes are as follows:

public/**, resources/**, static/**, templates/**, META-INF/**, *

The default excludes are as follows:

.*, repository/**, build/**, target/**, **/*.jar, **/*.groovy

Type spring help jar on the command line for more information.

2.4. Initialize a New Project

The init command lets you create a new project by using start.spring.io without leaving the shell, as shown in the following example:

$ spring init --dependencies=web,data-jpa my-project
Using service at https://start.spring.io
Project extracted to '/Users/developer/example/my-project'

The preceding example creates a my-project directory with a Maven-based project that uses spring-boot-starter-web and spring-boot-starter-data-jpa. You can list the capabilities of the service by using the --list flag, as shown in the following example:

$ spring init --list
=======================================
Capabilities of https://start.spring.io
=======================================

Available dependencies:
-----------------------
actuator - Actuator: Production ready features to help you monitor and manage your application
...
web - Web: Support for full-stack web development, including Tomcat and spring-webmvc
websocket - Websocket: Support for WebSocket development
ws - WS: Support for Spring Web Services

Available project types:
------------------------
gradle-build -  Gradle Config [format:build, build:gradle]
gradle-project -  Gradle Project [format:project, build:gradle]
maven-build -  Maven POM [format:build, build:maven]
maven-project -  Maven Project [format:project, build:maven] (default)

...

The init command supports many options. See the help output for more details. For instance, the following command creates a Gradle project that uses Java 8 and war packaging:

$ spring init --build=gradle --java-version=1.8 --dependencies=websocket --packaging=war sample-app.zip
Using service at https://start.spring.io
Content saved to 'sample-app.zip'

2.5. Using the Embedded Shell

Spring Boot includes command-line completion scripts for the BASH and zsh shells. If you do not use either of these shells (perhaps you are a Windows user), you can use the shell command to launch an integrated shell, as shown in the following example:

$ spring shell
Spring Boot (v2.2.1.RELEASE)
Hit TAB to complete. Type \'help' and hit RETURN for help, and \'exit' to quit.

From inside the embedded shell, you can run other commands directly:

$ version
Spring CLI v2.2.1.RELEASE

The embedded shell supports ANSI color output as well as tab completion. If you need to run a native command, you can use the ! prefix. To exit the embedded shell, press ctrl-c.

2.6. Adding Extensions to the CLI

You can add extensions to the CLI by using the install command. The command takes one or more sets of artifact coordinates in the format group:artifact:version, as shown in the following example:

$ spring install com.example:spring-boot-cli-extension:1.0.0.RELEASE

In addition to installing the artifacts identified by the coordinates you supply, all of the artifacts' dependencies are also installed.

To uninstall a dependency, use the uninstall command. As with the install command, it takes one or more sets of artifact coordinates in the format of group:artifact:version, as shown in the following example:

$ spring uninstall com.example:spring-boot-cli-extension:1.0.0.RELEASE

It uninstalls the artifacts identified by the coordinates you supply and their dependencies.

To uninstall all additional dependencies, you can use the --all option, as shown in the following example:

$ spring uninstall --all

3. Developing Applications with the Groovy Beans DSL

Spring Framework 4.0 has native support for a beans{} “DSL” (borrowed from Grails), and you can embed bean definitions in your Groovy application scripts by using the same format. This is sometimes a good way to include external features like middleware declarations, as shown in the following example:

@Configuration(proxyBeanMethods = false)
class Application implements CommandLineRunner {

    @Autowired
    SharedService service

    @Override
    void run(String... args) {
        println service.message
    }

}

import my.company.SharedService

beans {
    service(SharedService) {
        message = "Hello World"
    }
}

You can mix class declarations with beans{} in the same file as long as they stay at the top level, or, if you prefer, you can put the beans DSL in a separate file.

4. Configuring the CLI with settings.xml

The Spring Boot CLI uses Aether, Maven’s dependency resolution engine, to resolve dependencies. The CLI makes use of the Maven configuration found in ~/.m2/settings.xml to configure Aether. The following configuration settings are honored by the CLI:

  • Offline

  • Mirrors

  • Servers

  • Proxies

  • Profiles

    • Activation

    • Repositories

  • Active profiles

See Maven’s settings documentation for further information.

5. What to Read Next

There are some sample groovy scripts available from the GitHub repository that you can use to try out the Spring Boot CLI. There is also extensive Javadoc throughout the source code.

If you find that you reach the limit of the CLI tool, you probably want to look at converting your application to a full Gradle or Maven built “Groovy project”. The next section covers Spring Boot’s "Build tool plugins", which you can use with Gradle or Maven.