Corndel

Appearance

Making a CLI ​

Installing Picocli ​

We're going to be using Picocli to make our command line

To add this as a dependency in Maven, add the following dependency to the dependencies in your pom.xml

xml
<dependency>
  <groupId>info.picocli</groupId>
  <artifactId>picocli</artifactId>
  <version>4.7.6</version>
</dependency>

Setting up your CLI ​

In the main class, we set up picocli.CommandLine to process the command line args.

java
package com.corndel.healthtracker;

import picocli.CommandLine;
import picocli.CommandLine.Command;

@Command(name = "healthtracker", description = "A CLI health tracker")
public class App {

  public static void main(String[] args) {
    CommandLine cli = new CommandLine(new App());
    int exitCode = cli.execute(args);
    System.exit(exitCode);
  }

}

INFO

Picocli uses annotations to declare metadata.

Here, we use the @Command() annotation to declare the name and description of our healthtracker cli command.

Printing a message ​

To execute some code, we need to add a run() method, and also implement the Runnable interface.

java
@Command(name = "healthtracker", description = "A CLI health tracker")
public class App implements Runnable {

  @Override
  public void run() {
    System.out.println("Welcome! Please specify a command.")
  }

  public static void main(String[] args) {
    CommandLine cli = new CommandLine(new App());
    int exitCode = cli.execute(args);
    System.exit(exitCode);
  }

}

Now the run() method will run if the user simply executes healthtracker in the terminal.

console
> healthtracker

Welcome! Please specify a command.

Handling input arguments ​

The user can specify arguments to pass to the run() method. We configure the CLI to accept these using the @Parameters decorator. We can access them around our class.

java
@Command(name = "healthtracker", description = "A CLI health tracker")
public class App implements Runnable {

  @Parameters(index = "0", description = "The name to greet", defaultValue = "User")
  private String name;

  @Override
  public void run() {
    String msg = String.format("Welcome, %s! Please specify a command.", name);
    System.out.println(msg);
  }

  public static void main(String[] args) {
    CommandLine cli = new CommandLine(new App());
    int exitCode = cli.execute(args);
    System.exit(exitCode);
  }

}

Now the user can pass their name to the CLI to get a more personalised message.

console
> healthtracker Magnus

Welcome, Magnus! Please specify a command.

TIP

Note that we have include the defaultValue in the @Parameter field. If no name is given, this default value will be used instead.