1. Commands
In this section, we go through an actual command registration and leave command options and execution for later in a documentation. You can find more detailed info in [appendix-tech-intro-registration].
1.1. Registration
There are two different ways to define a command: through an annotation model and through a programmatic model. In the annotation model, you define your methods in a class and annotate the class and the methods with specific annotations. In the programmatic model, you use a more low level approach, defining command registrations (either as beans or by dynamically registering with a command catalog).
1.1.1. Annotation Model
When you use the standard API, methods on beans are turned into executable commands, provided that:
-
The bean class bears the
@ShellComponentannotation. (This is used to restrict the set of beans that are considered.) -
The method bears the
@ShellMethodannotation.
|
The You can customize the name of the created bean by using the |
@ShellComponent
static class MyCommands {
@ShellMethod
public void mycommand() {
}
}
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 start with a capital letter and end with a period. |
By default, you need not 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 (for example, 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. |
1.2. 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 be the best way to show the available commands.
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 camelCase class name into separate words (so URLRelatedCommands becomes URL Related Commands).
This is a 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:
-
Specify a
group()in the@ShellMethodannotation. -
Place a
@ShellCommandGroupon the class in which the command is defined. This applies the group for all commands defined in that class (unless overridden, as explained earlier). -
Place a
@ShellCommandGroupon the package (throughpackage-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() {}
}
1.3. 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 explain that
the command exists 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 use 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 |
Finally, 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
|
| 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. |
1.4. Exception Handling
Many command line applications when applicable return an exit code which running environment
can use to differentiate if command has been executed successfully or not. In a spring-shell
this mostly relates when a command is run on a non-interactive mode meaning one command
is always executed once with an instance of a spring-shell.
1.4.1. Exception Resolving
Unhandled exceptions will bubble up into shell’s ResultHandlerService and then eventually
handled by some instance of ResultHandler. Chain of ExceptionResolver implementations
can be used to resolve exceptions and gives you flexibility to return message to get written
into console together with exit code which are wrapped within CommandHandlingResult.
static class CustomExceptionResolver implements CommandExceptionResolver {
@Override
public CommandHandlingResult resolve(Exception e) {
if (e instanceof CustomException) {
return CommandHandlingResult.of("Hi, handled exception\n", 42);
}
return null;
}
}
CommandExceptionResolver implementations can be defined globally as beans or defined
per CommandRegistration if it’s applicable only for a particular command itself.
CommandRegistration.builder()
.withErrorHandling()
.resolver(new CustomExceptionResolver())
.and()
.build();
Use you own exception types which can also be an instance of boot’s ExitCodeGenerator if
you want to define exit code there.
static class CustomException extends RuntimeException {}
| With annotation based configuration exception resolving can only be customised globally |
1.4.2. Exit Code Mappings
Default behaviour of an exit codes is as:
-
Errors from a command option parsing will result code of
2 -
Any generic error will result result code of
1 -
Obviously in any other case result code is
0
Every CommandRegistration can define its own mappings between Exception and exit code.
Essentially we’re bound to functionality in Spring Boot regarding exit code and simply
integrate into that.
Assuming there is an exception show below which would be thrown from a command:
static class MyException extends RuntimeException {
private final int code;
MyException(String msg, int code) {
super(msg);
this.code = code;
}
public int getCode() {
return code;
}
}
It is possible to define a mapping function between Throwable and exit code. You can also
just configure a class to exit code which is just a syntactic sugar within configurations.
CommandRegistration.builder()
.withExitCode()
.map(MyException.class, 3)
.map(t -> {
if (t instanceof MyException) {
return ((MyException) t).getCode();
}
return 0;
})
.and()
.build();
| Exit codes cannot be customized with annotation based configuration |
1.5. Hidden Command
It is possible to hide a command which is convenient in cases where it is not yet ready for prime time, is meant for debugging purposes or you have any other reason you dont want to advertise its presense.
Hidden command can be executed if you know it and its options. It is effectively removed from:
-
Help listing
-
Help page for command return "unknown command"
-
Command completion in interactive mode
-
Bash completion
Below is an example how to define command as hidden. It shows available builder methods to define hidden state.
CommandRegistration commandRegistration() {
return CommandRegistration.builder()
.command("mycommand")
// define as hidden
.hidden()
// can be defined via a flag (false)
.hidden(false)
// can be defined via a flag (true)
.hidden(true)
.build();
}
| Defining hidden commands is not supported with annotation based configuration |
1.6. Interaction Mode
Command registration can define InteractionMode which is used to hide commands
depending which mode shell is executing. More about that in [using-shell-execution-interactionmode].
You can define it with CommandRegisration.
CommandRegistration commandRegistration() {
return CommandRegistration.builder()
.command("mycommand")
// can be defined for all modes
.interactionMode(InteractionMode.ALL)
// can be defined only for interactive
.interactionMode(InteractionMode.INTERACTIVE)
// can be defined only for non-interactive
.interactionMode(InteractionMode.NONINTERACTIVE)
.build();
}
Or with @ShellMethod.
@ShellMethod(key = "mycommand", interactionMode = InteractionMode.INTERACTIVE)
public void mycommand() {
}
1.7. Built-In Commands
1.7.1. 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:
my-shell:>help
AVAILABLE COMMANDS
Built-In Commands
exit: Exit the shell.
help: Display help about available commands
stacktrace: Display the full stacktrace of the last error.
clear: Clear the shell screen.
quit: Exit the shell.
history: Display or save the history of previously run commands
completion bash: Generate bash completion script
version: Show version info
script: Read and execute commands from a file.
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 following listing shows the help command applied to itself:
my-shell:>help help
NAME
help - Display help about available commands
SYNOPSIS
help --command String
OPTIONS
--command or -C String
The command to obtain help for.
[Optional]
Help is templated and can be customized if needed. Settings are under spring.shell.command.help where you can use
enabled to disable command, grouping-mode taking group or flat if you want to hide groups by flattening
a structure, command-template to define your template for output of a command help, commands-template to define
output of a command list.
If spring.shell.command.help.grouping-mode=flat is set, then help would show:
my-shell:>help help
AVAILABLE COMMANDS
exit: Exit the shell.
help: Display help about available commands
stacktrace: Display the full stacktrace of the last error.
clear: Clear the shell screen.
quit: Exit the shell.
history: Display or save the history of previously run commands
completion bash: Generate bash completion script
version: Show version info
script: Read and execute commands from a file.
Output from help and help <commmand> are both templated with a default implementation
which can be changed.
Option spring.shell.command.help.commands-template defaults to
classpath:template/help-commands-default.stg and is passed GroupsInfoModel
as a model.
Option spring.shell.command.help.command-template defaults to
classpath:template/help-command-default.stg and is passed CommandInfoModel
as a model.
| Key | Description |
|---|---|
|
|
|
The commands variables (see GroupCommandInfoModel Variables). |
|
The commands variables (see CommandInfoModel Variables). |
|
|
| Key | Description |
|---|---|
|
The name of a group, if set. Otherwise, empty. |
|
The commands, if set. Otherwise, empty. Type is a multi value, see CommandInfoModel Variables. |
| Key | Description |
|---|---|
|
The name of a command, if set. Otherwise, null. Type is string and contains full command. |
|
The names of a command, if set. Otherwise, null. Type is multi value essentially |
|
The possible aliases, if set. Type is multi value with strings. |
|
The description of a command, if set. Otherwise, null. |
|
The parameters variables, if set. Otherwise empty. Type is a multi value, see CommandParameterInfoModel Variables. |
|
The availability variables (see CommandAvailabilityInfoModel Variables). |
| Key | Description |
|---|---|
|
The type of a parameter if set. Otherwise, null. |
|
The arguments, if set. Otherwise, null. Type is multi value with strings. |
|
|
|
The description of a parameter, if set. Otherwise, null. |
|
The default value of a parameter, if set. Otherwise, null. |
|
|
| Key | Description |
|---|---|
|
|
|
The reason if not available if set. Otherwise, null. |
1.7.2. Clear
The clear command does what you would expect and clears the screen, resetting the prompt
in the top left corner.
1.7.3. 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 on the next launch.
1.7.4. 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.
1.7.5. 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.
1.7.6. History
The history command shows the history of commands that has been executed.
There are a few configuration options that you can use to configure behavior
of a history. History is kept in a log file, which is enabled by default and can
be turned off by setting spring.shell.history.enabled. The name of a log file
is resolved from spring.application.name and defaults to spring-shell.log,
which you can change by setting spring.shell.history.name.
By default, a log file is generated to a current working directory, which you can dictate
by setting spring.shell.config.location. This property can contain
a placeholder ({userconfig}), which resolves to a common shared config directory.
| Run the Spring Shell application to see how the sample application works as it uses these options. |
1.7.7. Completion
The completion command set lets you create script files that can be used
with am OS shell implementations to provide completion. This is very useful when
working with non-interactive mode.
Currently, the only implementation is for bash, which works with bash sub-command.
1.7.8. Version
The version command shows existing build and git info by integrating into
Boot’s BuildProperties and GitProperties if those exist in the shell application.
By default, only version information is shown, and you can enable other information through configuration
options.
The relevant settings are under spring.shell.command.version, where you can use enabled to
disable a command and, optionally, define your own template with template. You can use the
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 commands to control
fields in a default template.
The template defaults to classpath:template/version-default.st, and you can define
your own, as the following example shows:
<buildVersion>
This setting would output something like the following:
X.X.X
You can add the following attributes to the default template rendering: buildVersion, buildGroup,
buildGroup, buildName, buildTime, gitShortCommitId, gitCommitId,
gitBranch, and gitCommitTime.