2.1.0-M2

© 2017 - 2022 VMware, Inc.

Copies of this document may be made for your own use and for distribution to others, provided that you do not charge any fee for such copies and further provided that each copy contains this Copyright Notice, whether distributed in print or electronically.

1. What is Spring Shell?

Not all applications need a fancy web user interface! Sometimes, interacting with an application through an interactive terminal is the most appropriate way to get things done.

Spring Shell lets you create such a runnable application, where the user enters textual commands that are run until the program terminates. The Spring Shell project provides the infrastructure to create such a REPL (Read, Eval, Print Loop), letting you concentrate on the commands implementation by using the familiar Spring programming model.

Advanced features such as parsing, tab completion, colorization of output, fancy ascii-art table display, input conversion, and validation are all include, freeing you to focus on core command logic.

2. Using Spring Shell

This section describes how to use Spring Shell.

Spring Shell 2.1.x is a major rework to bring codebase up-to-date with existing Spring Boot versions, adding new features and especially making it work with GraalVM which makes command-line applications much more relevant on a java space. Moving to new major version also allows us to clean up codebase and make some needed breaking changes.

2.1. Getting Started

To see what Spring Shell has to offer, we can write a trivial shell application that has a simple command to add two numbers.

2.1.1. Writing a Simple Boot Application

Starting with version 2, Spring Shell has been rewritten from the ground up with various enhancements in mind, one of which is easy integration with Spring Boot, although it is not a strong requirement. For the purpose of this tutorial, we create a simple Boot application by using start.spring.io. This minimal application depends only on spring-boot-starter and configures the spring-boot-maven-plugin to generate an executable ├╝ber-jar:

...
<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter</artifactId>
    </dependency>
    ...
</dependencies>

2.1.2. Adding a Dependency on Spring Shell

The easiest way to get going with Spring Shell is to depend on the spring-shell-starter artifact. This comes with everything one needs to use Spring Shell and plays nicely with Boot, configuring only the necessary beans as needed:

...
<dependency>
    <groupId>org.springframework.shell</groupId>
    <artifactId>spring-shell-starter</artifactId>
    <version>2.1.0-M2</version>
</dependency>
...
Given that Spring Shell starts the REPL by virtue of this dependency being present, you need to either skip tests when you build (-DskipTests) throughout this tutorial or remove the sample integration test that was generated by start.spring.io. If you do not remove it, the integration test creates the Spring ApplicationContext and, depending on your build tool, stays stuck in the eval loop or crashes with a NPE.

2.1.3. Your First Command

Now we can add our first command. To do so, create a new class (named whatever you want) and annotate it with @ShellComponent (a variation of @Component that is used to restrict the set of classes that are scanned for candidate commands).

Then create an add method that takes two ints (a and b) and returns their sum. Annotate it with @ShellMethod and provide a description of the command in the annotation (the only piece of information that is required):

package com.example.demo;

import org.springframework.shell.standard.ShellMethod;
import org.springframework.shell.standard.ShellComponent;

@ShellComponent
public class MyCommands {

    @ShellMethod("Add two integers together.")
    public int add(int a, int b) {
        return a + b;
    }
}

2.1.4. Trying the Application

To build the application and run the generated jar, run the following command:

./mvnw clean install -DskipTests
[...]

java -jar target/demo-0.0.1-SNAPSHOT.jar

You are greeted by the following screen (the banner comes from Spring Boot and can be customized:

shell:>

A yellow shell:> prompt invites you to type commands. Type add 1 2, press ENTER, and admire the magic:

shell:>add 1 2
3

Try to play with the shell (hint: there is a help command). When you are done, type exit and press ENTER.

The rest of this document delves deeper into the whole Spring Shell programming model.

2.2. Writing Your Own Commands

The way Spring Shell decides to turn a method into an actual shell command is entirely pluggable (see [extending-spring-shell]). However, as of Spring Shell 2.x, the recommended way to write commands is to use the new API described in this section (the standard API).

When you use the standard API, methods on beans are turned into executable commands, provided that:

  • The bean class bears the @ShellComponent annotation. This is used to restrict the set of beans that are considered.

  • The method bears the @ShellMethod annotation.

The @ShellComponent is a stereotype annotation that is itself meta-annotated with @Component. As a result, you can used it in addition to the filtering mechanism to declare beans (for example, by using @ComponentScan).

You can customize the name of the created bean by using the value attribute of the annotation.

2.2.1. Documenting the Command

The only required attribute of the @ShellMethod annotation is its value attribute, which should have a short, one-sentence, description of what the command does. This lets your users get consistent help about your commands without having to leave the shell (see Help).

The description of your command should be short — no more than one or two sentences. For better consistency, it should starts with a capital letter and end with a period.

2.2.2. Customizing the Command Name(s)

By default, there is no need to specify the key for your command (that is, the word(s) that should be used to invoke it in the shell). The name of the method is used as the command key, turning camelCase names into dashed, gnu-style, names (that is, sayHello() becomes say-hello).

You can, however, explicitly set the command key, by using the key attribute of the annotation:

	@ShellMethod(value = "Add numbers.", key = "sum")
	public int add(int a, int b) {
		return a + b;
	}
The key attribute accepts multiple values. If you set multiple keys for a single method, the command is registered with those different aliases.
The command key can contain pretty much any character, including spaces. When coming up with names though, keep in mind that consistency is often appreciated by users (that is, you should avoid mixing dashed-names with spaced names and other inconsistencies).

2.3. Invoking your Commands

This section addresses how you can control the way in which your commands are invoked.

2.3.1. By Name Versus Positional Parameters

As seen earlier, decorating a method with @ShellMethod is the sole requirement for creating a command.

The user can set the value of all the method parameters in either of two ways:

  • By using a parameter key (for example, --arg value). This approach is called “by name parameters.”

  • Without a key, by setting parameter values in the order in which they appear in the method signature (called “positional parameters”).

These two approaches can be mixed and matched, with named parameters always taking precedence (as they are less prone to ambiguity). Consider the following command definition:

	@ShellMethod("Display stuff.")
	public String echo(int a, int b, int c) {
		return String.format("You said a=%d, b=%d, c=%d", a, b, c);
	}

Given the preceding command definiton, the following invocations are all equivalent, as shown in the output:

shell:>echo 1 2 3               (1)
You said a=1, b=2, c=3

shell:>echo --a 1 --b 2 --c 3   (2)
You said a=1, b=2, c=3

shell:>echo --b 2 --c 3 --a 1   (3)
You said a=1, b=2, c=3

shell:>echo --a 1 2 3           (4)
You said a=1, b=2, c=3

shell:>echo 1 --c 3 2           (5)
You said a=1, b=2, c=3
1 This uses positional parameters.
2 This is an example of full by-name parameters.
3 By-name parameters can be reordered as desired.
4 You can use a mix of the two approaches.
5 The non by-name parameters are resolved in the order in which they appear.
Customizing the Named Parameter Keys

As seen earlier, the default strategy for deriving the key for a named parameter is to use the Java name of the method signature and prefix it with two dashes (--). You can customize this in two ways:

  • Use the prefix() attribute of the @ShellMethod annotation to change the default prefix for the whole method.

  • Annotate the parameter with the @ShellOption annotation to override the entire key in a per-parameter fashion.

Consider the following example:

	@ShellMethod(value = "Display stuff.", prefix="-")
	public String echo(int a, int b, @ShellOption("--third") int c) {
		return String.format("You said a=%d, b=%d, c=%d", a, b, c);
	}

For such a setup, the possible parameter keys are -a, -b and --third.

You can specify several keys for a single parameter. If you do so, these keys are mutually exclusive (only one of them can be used) ways to specify the same parameter. The following example shows the signature of the built-in help command:

	@ShellMethod("Describe a command.")
	public String help(@ShellOption({"-C", "--command"}) String command) {
		...
	}

2.3.2. Optional Parameters and Default Values

Spring Shell provides the ability to give parameters default values, which lets users omit those parameters. Consider the following command definition:

	@ShellMethod("Say hello.")
	public String greet(@ShellOption(defaultValue="World") String who) {
		return "Hello " + who;
	}

With the preceding definition, the greet command can still be invoked as greet Mother (or greet --who Mother), but the following is also possible:

shell:>greet
Hello World

2.3.3. Parameter Arity

Up to now, it has always been assumed that each parameter maps to a single word entered by the user. Situations may arise, though, when a parameter value should be multi-valued. This is driven by the arity() attribute of the @ShellOption annotation. You can use a collection or array for the parameter type and specify how many values are expected:

	@ShellMethod("Add Numbers.")
	public float add(@ShellOption(arity=3) float[] numbers) {
		return numbers[0] + numbers[1] + numbers[2];
	}

The users can then invoke the command by using any of the following syntax:

shell:>add 1 2 3.3
6.3
shell:>add --numbers 1 2 3.3
6.3

When using the by-name parameter approach, the key should not be repeated. The following does not work:

shell:>add --numbers 1 --numbers 2 --numbers 3.3
Varying Amount Arity

The above example demonstrates requiring a known, constant arity for a parameter, three in this case. Allowing any number of multiple values of a parameter can be achieved by leaving arity unspecified and using Spring’s built-in comma separated value parsing for collections and/or arrays:

	@ShellMethod("Add a Varying Amount of Numbers.")
	public double add(@ShellOption double[] numbers) {
		return Arrays.stream(numbers).sum();
	}

The command may then be invoked with any amount of numbers:

shell:>add 1,2,3.3
6.3
shell:>add --numbers 42
42.0
shell:>add --numbers 1,2,3.3,4,5
15.3
Special Handling of Boolean Parameters

When it comes to parameter arity, one kind of parameter receives a special treatment by default, as is often the case in command-line utilities. Boolean (that is, boolean as well as java.lang.Boolean) parameters behave like they have an arity() of 0 by default, allowing users to set their values by using a “flag” approach. Consider the following command definition:

	@ShellMethod("Terminate the system.")
	public String shutdown(boolean force) {
		return "You said " + force;
	}

This preceding command definition allows the following invocations:

shell:>shutdown
You said false
shell:>shutdown --force
You said true
This special treatment plays well with the default value specification. Although the default for boolean parameters is to have their default value be false, you can specify otherwise (that is, @ShellOption(defaultValue="true")), and the behavior is inverted (that is, not specifying the parameter results in the value being true, and specifying the flag results in the value being false)

Having this behavior of implicit arity()=0 prevents the user from specifying a value (for example, shutdown --force true). If you would like to allow this behavior (and forego the flag approach), then force an arity of 1 by using the annotation as follows:

	@ShellMethod("Terminate the system.")
	public String shutdown(@ShellOption(arity=1, defaultValue="false") boolean force) {
		return "You said " + force;
	}

2.3.4. Quotes Handling

Spring Shell takes user input and tokenizes it into words, splitting on space characters. If the user wants to provide a parameter value that contains spaces, that value needs to be quoted. Both single (') and double (") quotes are supported, and those quotes are not part of the value: Consider the following command definition:

	@ShellMethod("Prints what has been entered.")
	public String echo(String what) {
		return "You said " + what;
	}

The following commands all invoke the preceding command definition:

shell:>echo Hello
You said Hello
shell:>echo 'Hello'
You said Hello
shell:>echo 'Hello World'
You said Hello World
shell:>echo "Hello World"
You said Hello World

Supporting both single and double quotes lets the user embed one type of quotes into a value:

shell:>echo "I'm here!"
You said I'm here!
shell:>echo 'He said "Hi!"'
You said He said "Hi!"

That way, the user can use a single quote as an apostrophe in a message.

Should the user need to embed the same kind of quote that was used to quote the whole parameter, the escape sequence uses the backslash (\) character:

shell:>echo 'I\'m here!'
You said I'm here!
shell:>echo "He said \"Hi!\""
You said He said "Hi!"
shell:>echo I\'m here!
You said I'm here!

It is also possible to escape space characters when not using enclosing quotes:

shell:>echo This\ is\ a\ single\ value
You said This is a single value

2.3.5. Interacting with the Shell

The Spring Shell project builds on top of the JLine library and, as a result, brings a lot of nice interactive features, some of which are detailed in this section.

First and foremost, Spring Shell supports tab completion almost everywhere possible. So, if there is an echo command and the user types ec and presses TAB, echo appears. Should there be several commands that start with ec, then the user is prompted to choose (using TAB or Shift + TAB to navigate and ENTER to select.)

But completion does not stop at command keys. It also works for parameter keys (--arg) and even parameter values, if the application developer registered the appropriate beans (see [providing-tab-completion]).

Another nice feature of Spring Shell applications is support for line continuation. If a command and its parameters is too long and does not fit nicely on the screen, a user can chunk it by ending a line with a backslash (\) character, pressing ENTER, and continuing on the next line. Upon submission of the whole command, this is parsed as if the user entered a single space on line breaks. The following listing shows an example of this behavior:

shell:>register module --type source --name foo  \ (1)
> --uri file:///tmp/bar
Successfully registered module 'source:foo'
1 command continues on next line

Line continuation also automatically triggers if the user has opened a quote (see Quotes Handling) and presses ENTER while still in the quotes:

shell:>echo "Hello (1)
dquote> World"
You said Hello World
1 The user pressed ENTER here.

Finally, Spring Shell applications benefit from a lot of keyboard shortcuts (borrowed from Emacs) with which you may already be familiar from working with your regular OS Shell. Notable shortcuts include Ctrl+r to perform a reverse search, Ctrl+a] and Ctrl+e to move to the beginning and the end of the current line (respectively), and Esc f and Esc b to move forward or backward (respectively) one word at a time.

2.4. Validating Command Arguments

Spring Shell integrates with the Bean Validation API to support automatic and self-documenting constraints on command parameters.

Annotations found on command parameters as well as annotations at the method level are honored and trigger validation prior to the command executing. Consider the following command:

	@ShellMethod("Change password.")
	public String changePassword(@Size(min = 8, max = 40) String password) {
		return "Password successfully set to " + password;
	}

From the preceding example, you get the following behavior for free:

shell:>change-password hello
The following constraints were not met:
	--password string : size must be between 8 and 40 (You passed 'hello')
Applies to All Command Implementations
It is important to note that bean validation applies to all command implementations, whether they use the "standard" API or any other API, through the use of an adapter (see Supporting Other APIs)

2.5. Dynamic Command Availability

Registered commands do not always make sense, due to the internal state of the application. For example, there may be a download command, but it only works once the user has used connect on a remote server. Now, if the user tries to use the download command, the shell should gracefully explain that the command exist but that it is not available at the time. Spring Shell lets you do that, even letting you provide a short explanation of the reason for the command not being available.

There are three possible ways for a command to indicate availability. They all leverage a no-arg method that returns an instance of Availability. Consider the following example:

@ShellComponent
public class MyCommands {

    private boolean connected;

    @ShellMethod("Connect to the server.")
    public void connect(String user, String password) {
        [...]
        connected = true;
    }

    @ShellMethod("Download the nuclear codes.")
    public void download() {
        [...]
    }

    public Availability downloadAvailability() {
        return connected
            ? Availability.available()
            : Availability.unavailable("you are not connected");
    }
}

The connect method is used to connect to the server (details omitted), altering the state of the command through the connected boolean when done. The download command as marked as unavailable until the user has connected, thanks to the presence of a method named exactly as the download command method with the Availability suffix in its name. The method returns an instance of Availability, constructed with one of the two factory methods. If the command is not available, an explanation has to be provided. Now, if the user tries to invoke the command while not being connected, here is what happens:

shell:>download
Command 'download' exists but is not currently available because you are not connected.
Details of the error have been omitted. You can use the stacktrace command to print the full stacktrace.

Information about currently unavailable commands is also used in the integrated help. See Help.

The reason provided when the command is not available should read nicely if appended after “Because”.

You should not start the sentence with a capital or add a final period

If naming the availability method after the name of the command method does not suit you, you can provide an explicit name by using the @ShellMethodAvailability annotation:

    @ShellMethod("Download the nuclear codes.")
    @ShellMethodAvailability("availabilityCheck") (1)
    public void download() {
        [...]
    }

    public Availability availabilityCheck() { (1)
        return connected
            ? Availability.available()
            : Availability.unavailable("you are not connected");
    }
1 the names have to match

Lastly, it is often the case that several commands in the same class share the same internal state and, thus, should all be available or unavailable as a group. Instead of having to stick the @ShellMethodAvailability on all command methods, Spring Shell lets you flip things around and put the @ShellMethodAvailabilty annotation on the availability method, specifying the names of the commands that it controls:

    @ShellMethod("Download the nuclear codes.")
    public void download() {
        [...]
    }

    @ShellMethod("Disconnect from the server.")
    public void disconnect() {
        [...]
    }

    @ShellMethodAvailability({"download", "disconnect"})
    public Availability availabilityCheck() {
        return connected
            ? Availability.available()
            : Availability.unavailable("you are not connected");
    }

The default value for the @ShellMethodAvailability.value() attribute is *. This special wildcard matches all command names. This makes it easy to turn all commands of a single class on or off with a single availability method:

@ShellComponent
public class Toggles {
  @ShellMethodAvailability
  public Availability availabilityOnWeekdays() {
    return Calendar.getInstance().get(DAY_OF_WEEK) == SUNDAY
      ? Availability.available()
      : Availability.unavailable("today is not Sunday");
  }

  @ShellMethod
  public void foo() {}

  @ShellMethod
  public void bar() {}
}
Spring Shell does not impose many constraints on how to write commands and how to organize classes. However, it is often good practice to put related commands in the same class, and the availability indicators can benefit from that.

2.6. Organizing Commands

When your shell starts to provide a lot of functionality, you may end up with a lot of commands, which could be confusing for your users. By typing help, they would see a daunting list of commands, organized in alphabetical order, which may not always make sense.

To alleviate this possible confusion, Spring Shell provides the ability to group commands together, with reasonable defaults. Related commands would then end up in the same group (for example, User Management Commands) and be displayed together in the help screen and other places.

By default, commands are grouped according to the class they are implemented in, turning the camel case class name into separate words (so URLRelatedCommands becomes URL Related Commands). This is a very sensible default, as related commands are often already in the class anyway, because they need to use the same collaborating objects.

If, however, this behavior does not suit you, you can override the group for a command in the following ways, in order of priority:

  1. Specifying a group() in the @ShellMethod annotation.

  2. Placing a @ShellCommandGroup on the class in which the command is defined. This applies the group for all commands defined in that class (unless overridden, as explained earlier).

  3. Placing a @ShellCommandGroup on the package (through package-info.java) in which the command is defined. This applies to all the commands defined in the package (unless overridden at the method or class level, as explained earlier)

The following listing shows an example:

public class UserCommands {
    @ShellMethod(value = "This command ends up in the 'User Commands' group")
    public void foo() {}

    @ShellMethod(value = "This command ends up in the 'Other Commands' group",
    	group = "Other Commands")
    public void bar() {}
}

...

@ShellCommandGroup("Other Commands")
public class SomeCommands {
	@ShellMethod(value = "This one is in 'Other Commands'")
	public void wizz() {}

	@ShellMethod(value = "And this one is 'Yet Another Group'",
		group = "Yet Another Group")
	public void last() {}
}

2.7. Built-In Commands

Any application built by using the spring-shell-starter artifact (or, to be more precise, the spring-shell-standard-commands dependency) comes with a set of built-in commands. You can override or disable these commands individually (see Overriding or Disabling Built-In Commands). However, if they are not overridden or disabled, this section describes their behavior.

2.7.1. Help

Running a shell application often implies that the user is in a graphically limited environment. Also, while we are nearly always connected in the era of mobile phones, accessing a web browser or any other rich UI application (such as a PDF viewer) may not always be possible. This is why it is important that the shell commands are correctly self documented, and this is where the help command comes in.

Typing help + ENTER lists all the commands known to the shell (including unavailable commands) and a short description of what they do, similar to the following:

shell:>help
AVAILABLE COMMANDS
        add: Add numbers together.
      * authenticate: Authenticate with the system.
      * blow-up: Blow Everything up.
        clear: Clear the shell screen.
        connect: Connect to the system
        disconnect: Disconnect from the system.
        exit, quit: Exit the shell.
        help: Display help about available commands.
        register module: Register a new module.
        script: Read and execute commands from a file.
        stacktrace: Display the full stacktrace of the last error.

Commands marked with (*) are currently unavailable.
Type `help <command>` to learn more.

Typing help <command> shows more detailed information about a command, including the available parameters, their type, whether they are mandatory or not, and other details.

The follwoing listing shows the help command applied to itself:

shell:>help help


NAME
	help - Display help about available commands.

SYNOPSYS
	help [[-C] string]

OPTIONS
	-C or --command  string
		The command to obtain help for.  [Optional, default = <none>]

2.7.2. Clear

The clear command does what you would expect and clears the screen, resetting the prompt in the top left corner.

2.7.3. Exit

The quit command (also aliased as exit) requests the shell to quit, gracefully closing the Spring application context. If not overridden, a JLine History bean writes a history of all commands to disk, so that they are available again (see Interacting with the Shell) on the next launch.

2.7.4. Stacktrace

When an exception occurs inside command code, it is caught by the shell and a simple, one-line message is displayed so as not to overflow the user with too much information. There are cases though when understanding what exactly happened is important (especially if the exception has a nested cause).

To this end, Spring Shell remembers the last exception that occurred, and the user can later use the stacktrace command to print all the details on the console.

2.7.5. Script

The script command accepts a local file as an argument and replays commands found there, one at a time.

Reading from the file behaves exactly like inside the interactive shell, so lines starting with // are considered to be comments and are ignored, while lines ending with \ trigger line continuation.

2.7.6. History

The history command shows history of a commands which has been executed.

2.7.7. Completion

The completion command set allows you to create scripts files which can be used with am OS shell implementations to provide completion. This is very usefull when working with non-interactive mode.

Currently only implementation is for bash which works with bash sub-command.

2.7.8. Version

The version command shows existing build and git info by integrating into Boot’s BuildProperties and GitProperties if those exists in a shell app. On default only version info is shown and other can be enabled via configuration options.

Settings are under spring.shell.command.version where you can use enabled to disable command and optionally define your own template with template. Options show-build-artifact, show-build-group, show-build-name, show-build-time, show-build-version, show-git-branch, show-git-commit-id, show-git-short-commit-id and show-git-commit-time can be used to control fields in a default template.

Template default to classpath:template/version-default.st and you can define your own, for example having:

<buildVersion>

Which would simply output something like:

X.X.X

Attributes added to default template rendering are buildVersion, buildGroup, buildGroup, buildName, buildTime, gitShortCommitId, gitCommitId, gitBranch and gitCommitTime.

2.8. Interaction Mode

Starting from 2.1.x a build-in support has been added to distinguish between interactive and non-interactive modes. This has been added so that it’s easier to use shell as a simple command-line tool without requiring customisation to accomplish that.

Currently interactive mode is entered if any command line options are passed when starting or running a shell from a command-line. This especially works well when shell application is compiled with Native Support.

Some commands may not have any usefull meaning if running on interactive mode or vice versa on non-interactive mode. For example a build-in exit command have no meaning in non-interactive mode as it’s used to exit interactive mode.

Annotation @ShellMethod has a field interactionMode which can be used to instruct shell when particular command is available.

2.9. Native Support

Re-work with 2.1.x brings in an experimental support for compiling shell application into native application with GraalVM and spring-native. As underlying jline library works with GraalVM most of a things should just work.

Project can be compiled with native profile to get sample compiled as an native application:

$ ./mvnw clean package -Pnative

You can then run sample either with interactive or non-interactive mode:

$ ./spring-shell-samples/target/spring-shell-samples help
AVAILABLE COMMANDS

Built-In Commands
        completion bash: Generate bash completion script
        help: Display help about available commands.
        history: Display or save the history of previously run commands
        script: Read and execute commands from a file.
...

2.10. Styling

Starting with 2.1.x there is a support for centrally handling styling and theming. There is a default theme named default which can be changed using property spring.shell.theme.name.

To create a new theme register new Theme bean with custom ThemeSettings where you can tweak styles.

@Configuration
static class CustomThemeConfig {

	@Bean
	public Theme myTheme() {
		return new Theme() {
			@Override
			public String getName() {
				return "mytheme";
			}
			@Override
			public ThemeSettings getSettings() {
				return new MyThemeSettings();
			}
		};
	}
}

static class MyThemeSettings extends ThemeSettings {
}

ThemeResolver can be used to resolve styles if you want to create jline styled strings programmatically.

@Autowired
private ThemeResolver themeResolver;

String resolvedStyle = themeResolver.resolveTag(TAG_TITLE);
AttributedStyle style = themeResolver.resolveStyle(resolvedStyle);

2.11. Customizing the Shell

2.11.1. Overriding or Disabling Built-In Commands

Spring Shell provides Built-in commands to let people achieve everyday tasks that many if not all shell applications need. If you are not happy with the way they behave, though, you can disable or override them, as explained in this section.

Disabling all Built-in Commands

If you do not need built-in commands at all, there is an easy way to “disable” them: don’t include them. Either use a maven exclusion on spring-shell-standard-commands or, if you are selectively including Spring Shell dependencies, don’t include that one in. The follwoing example shows how to exclude spring-shell-standard-commands:

<dependency>
    <groupId>org.springframework.shell</groupId>
    <artifactId>spring-shell-starter</artifactId>
    <version>2.1.0-M2</version>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.shell</groupId>
            <artifactId>spring-shell-standard-commands</artifactId>
        </exclusion>
    </exclusions>
</dependency>
Disabling Specific Commands

To disable a single built-in command, set the spring.shell.command.<command>.enabled property to false in the application Environment. One way to do so is to pass extra arguments to the Boot application in your main() entry point:

	public static void main(String[] args) throws Exception {
		String[] disabledCommands = {"--spring.shell.command.help.enabled=false"}; (1)
		String[] fullArgs = StringUtils.concatenateStringArrays(args, disabledCommands);
		SpringApplication.run(MyApp.class, fullArgs);
	}
1 This disables the integrated help command
Overriding Specific Commands

If, instead of disabling a command, you would rather provide your own implementation, then you can either:

  • Disable the command as explained earlier and have your implementation registered with the same name.

  • Have your implementing class implement the <Command>.Command interface. As an example, here is how to override the clear command:

    public class MyClear implements Clear.Command {
    
        @ShellMethod("Clear the screen, only better.")
        public void clear() {
            // ...
        }
    }
Please Consider Contributing your Changes

If you feel like your implementation of a standard command could be valuable to the community, please open a pull-request at github.com/spring-projects/spring-shell.

Alternatively, before making any changes on your own, you can open an issue with the project. Feedback is always welcome!

2.11.2. PromptProvider

After each command invocation, the shell waits for new input from the user, displaying a prompt in yellow:

shell:>

It is possible to customize this behavior by registering a bean of type PromptProvider. Such a bean may use internal state to decide what to display to the user (it may, for example, react to application events) and can use JLine’s AttributedCharSequence to display fancy ANSI text.

The following example shows how to use a PromptProvider:

@Component
public class CustomPromptProvider implements PromptProvider {

	private ConnectionDetails connection;

	@Override
	public AttributedString getPrompt() {
		if (connection != null) {
			return new AttributedString(connection.getHost() + ":>",
				AttributedStyle.DEFAULT.foreground(AttributedStyle.YELLOW));
		}
		else {
			return new AttributedString("server-unknown:>",
				AttributedStyle.DEFAULT.foreground(AttributedStyle.RED));
		}
	}

	@EventListener
	public void handle(ConnectionUpdatedEvent event) {
		this.connection = event.getConnectionDetails();
	}
}

2.11.3. Customizing Command Line Options Behavior

There can be exactly one shell spesific ShellApplicationRunner which simply extends Boot’s ApplicationRunner. Default behariour is to have actual runner logic in various ShellRunner implementations where candidate will be picked up.

This is a breaking change in 2.1.x as previous shell versions had an confusing logic how ApplicationRunner instances were used. These changes were made to have a better support for interactive and non-interactive modes in a same shell application as it’s convenient to fully work on command-line and still have ability to enter interactive mode.

You can override bean type of ShellApplicationRunner if there’s a need to customise shell running logic.

====

==== Customizing Arguments Conversion

Conversion from text input to actual method arguments uses the standard Spring
https://docs.spring.io/spring/docs/4.3.11.RELEASE/spring-framework-reference/htmlsingle/#core-convert[conversion] mechanism.
Spring Shell installs a new `DefaultConversionService` (with built-in converters enabled)
and registers to it any bean of type `Converter<S, T>`, `GenericConverter`, or
`ConverterFactory<S, T>` that it finds in the application context.

This means that you can customize conversion to your custom objects
by installing a `Converter<String, Foo>` bean in the context:

====
[source, java]

@ShellComponent class ConversionCommands {

@ShellMethod("Shows conversion using Spring converter")
public String conversionExample(DomainObject object) {
	return object.getClass();
}

}

class DomainObject { private final String value;

DomainObject(String value) {
	this.value = value;
}
	public String toString() {
		return value;
	}
}

@Component class CustomDomainConverter implements Converter<String, DomainObject> {

	@Override
	public DomainObject convert(String source) {
		return new DomainObject(source);
	}
}
====

[TIP]
.Mind your String representation
=====
As in the preceding example, you should have
your `toString()` implementations return the converse of what was used
to create the object instance. This is because, when a value fails
validation, Spring Shell prints:

====
[source]

The following constraints were not met: --arg <type> : <message> (You passed '<value.toString()>')

====

See <<validating-command-arguments>> for more information.
=====

[NOTE]
====
If you want to customize the `ConversionService` further, you can:

* Have the default one injected in your code and act upon it in some way.
* Override it altogether with your own (custom converters need to be registered by hand).
  The `ConversionService` used by Spring Shell needs to be https://docs.spring.io/spring/docs/4.3.12.RELEASE/spring-framework-reference/htmlsingle/#beans-autowired-annotation-qualifiers[qualified] as `"spring-shell"`.
====

//==== Overriding the JLine Parser

//=== Using Without Spring Boot

// include::extending-spring-shell.adoc[]