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 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 v2.4.10
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:
@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 |
---|---|
|
JDBC Application. |
|
JMS Application. |
|
Caching abstraction. |
|
JUnit. |
|
RabbitMQ. |
extends |
Spock test. |
|
Spring Batch. |
|
Spring Integration. |
|
Spring MVC + Embedded Tomcat. |
|
Spring Security. |
|
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 (v2.4.10) 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 v2.4.10
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.