How can I update the Spring shell prompt without invoking a shell command?

2 min read 21-10-2024

How can I update the Spring shell prompt without invoking a shell command?

When working with Spring Shell, you might find yourself needing to update the shell prompt dynamically without the need to invoke a shell command. This capability can enhance the user experience by providing context-aware prompts that reflect the application's state. In this article, we will explore how to accomplish this, starting with the original code scenario.

Original Code Scenario

Imagine you have a Spring Shell application, and you want to modify the prompt displayed to the user based on certain conditions. Below is a simple example of how a typical Spring Shell setup might look:

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

@ShellComponent
public class MyCommands {

    @ShellMethod("Show hello")
    public String hello() {
        return "Hello, Spring Shell!";
    }
}

In this scenario, the default shell prompt would be something like shell>. However, we want to change this dynamically based on specific commands or application state without needing to invoke additional shell commands.

Updating the Spring Shell Prompt Dynamically

To update the Spring Shell prompt dynamically, you can use the PromptProvider interface. Here’s how you can do that:

Create a Custom PromptProvider: You need to implement the PromptProvider interface, which allows you to control the appearance of the prompt.
Inject the Context: Utilize the ApplicationContext to retrieve necessary beans or information that might influence the prompt.
Update the Prompt: Modify the getPrompt method to return a custom prompt based on the current application state.

Here's an example of how you can implement this:

import org.springframework.context.annotation.Bean;
import org.springframework.shell.PromptProvider;
import org.springframework.shell.standard.ShellComponent;
import org.springframework.shell.standard.ShellMethod;

@ShellComponent
public class MyCommands {

    private String userStatus = "User";

    @ShellMethod("Show hello")
    public String hello() {
        return "Hello, Spring Shell!";
    }

    public void setUserStatus(String status) {
        this.userStatus = status;
    }

    @Bean
    public PromptProvider customPromptProvider() {
        return () -> {
            return userStatus + ">";
        };
    }
}

Explanation of the Code

Custom PromptProvider: By creating a PromptProvider bean, you can control what the prompt displays. In this case, it will return the current user status followed by >.
Dynamic Update: The prompt updates dynamically based on the userStatus variable. You can create methods that modify this variable based on user input, allowing the prompt to reflect various states (e.g., "Admin>", "Guest>").

Practical Examples

Context-Aware Prompts: If your application has different user roles, you can set the prompt to reflect the current role. For example, an admin might have a different prompt than a regular user.
Task-Specific Prompts: If your application handles multiple tasks, you can set the prompt to include the current task, like "Backup>" when the user is in the backup process.
Session Information: Include session-specific information, like the active environment (development, testing, production), to inform the user of the current working context.

Conclusion

Updating the Spring Shell prompt dynamically without invoking shell commands is a straightforward process that can greatly enhance your application's usability. By implementing a custom PromptProvider, you can provide users with contextually relevant prompts that adapt to their actions and roles within your application.

Additional Resources

By following the guidelines above, you can create a more intuitive and engaging command-line interface with Spring Shell.