Argument Handling in Spring Shell

Introduction

Argument handling is a vital aspect of creating interactive command-line applications using Spring Shell. It allows users to input parameters when they run commands, enabling dynamic behavior based on user input. This tutorial will walk you through the basics of argument handling in Spring Shell, covering how to define commands, accept arguments, and handle various data types.

Setting Up Spring Shell

To get started with Spring Shell, you need to set up a Spring Boot project. You can use Spring Initializr to bootstrap a new project with the necessary dependencies.

Creating Your First Command

In Spring Shell, commands are defined using the @ShellComponent annotation. You can create a simple command that takes an argument by following the structure below:

@ShellComponent
public class GreetingCommands {
    
    @ShellMethod("Greets the user with the given name")
    public String greet(@ShellOption String name) {
        return "Hello, " + name + "!";
    }
}
                

In this example, the greet command takes one argument: name. The @ShellOption annotation indicates that this parameter is required when executing the command.

Running Commands

To run your command, execute the Spring Boot application. You can then type the command in the shell, followed by the required argument.

greet --name Alice
                

Handling Multiple Arguments

You can also define commands that accept multiple arguments. Here's an example of a command that takes both a name and an age:

@ShellComponent
public class UserCommands {
    
    @ShellMethod("Creates a user with a name and age")
    public String createUser(@ShellOption String name, @ShellOption int age) {
        return "User " + name + " has been created with age " + age + ".";
    }
}
                

With this command, you can specify both the name and age when executing it.

Default Values and Optional Arguments

Spring Shell allows you to specify default values for arguments. You can also make arguments optional by using the defaultValue attribute.

@ShellComponent
public class DefaultCommands {
    
    @ShellMethod("Displays a message with an optional greeting")
    public String sayHello(@ShellOption(defaultValue = "World") String name) {
        return "Hello, " + name + "!";
    }
}
                

In this case, if no name is provided, it will default to "World":

sayHello
                

Conclusion

In this tutorial, we explored the fundamentals of argument handling in Spring Shell. We learned how to create commands that accept user input, handle multiple arguments, and set default values. This foundation will help you build more interactive and user-friendly command-line applications with Spring Shell.

For more advanced features and options, consider exploring the Spring Shell documentation.