Gfrktyl

I wrote got a lot of mini apps. Each app has it's own InputHandler for Input from the keyboard. It's time to make a lib for that purpose - a CommandLineInterface.

Can you review my code on

• Design


• OOP


• Clean Code


• Naming (my bad englisch leads to bad naming)

Interface CommandLineInterpreter

any class that implements this interface can be use the CommandLineInterface. M is the application, which implements the CommandLineInterpreter

public interface CommandLineInterpreter<M> { 

    Set<Command<M>> getCommands();

    Response executeCommand(String identifier, List<String> parameter);

}

Class Command

the Commandis responible to map in command typed via CLI into an action (method-call) on your app. To execute the command the Class is generic on M (which is your app) so you can call these app-specific methods.

public abstract class Command<M> {



    private final String identifier;



    public Command(String identifier) {

        this.identifier = identifier;

    }



    public abstract Response execute(M invoked, List<String> parameter);



    public String getIdentifier() {

        return identifier;

    }



    public boolean isIdentifier(String ident) {

        return identifier.equals(ident);

    }



    @Override

    public boolean equals(Object o) {

        if (this == o) return true;

        if (o == null || getClass() != o.getClass()) return false;

        Command command = (Command) o;

        return Objects.equals(identifier, command.identifier);

    }



    @Override

    public int hashCode() {

        return Objects.hash(identifier);

    } 

}

Class Response

provides information if the execution of an command was successful or not.

public class Response {

    private final String message;

    private final String details;

    private final Type type;



    private Response(Type type, String message, String details) {

        this.type = type;

        this.message = message;

        this.details = details;

    }



    public static Response fail(String message) {

        return fail(message, "");

    }



    public static Response fail(String message, String details) {

        return response(Type.FAILURE, message, details);

    }



    private static Response response(Type type, String message, String details) {

        return new Response(type, message, details);

    }



    public static Response success() {

        return success("ok", "");

    }



    public static Response success(String message) {

        return success(message, "");

    }



    public static Response success(String message, String details) {

        return response(Type.SUCCESS, message, details);

    }



    public boolean failed() {

        return type == Type.FAILURE;

    }



    @Override

    public String toString() {

        return type.toString() + ":" + message + (details.isEmpty() ? "" : " 

Details: " + details);

    }



    private enum Type {SUCCESS, FAILURE}

Class CommandLineInterface

this class handles the user input fromm command line. it is itself an CommandLineInterpreter and offers two basic commands: help and exit.

public class CommandLineInterface implements CommandLineInterpreter<CommandLineInterface> {



    private static final String COMMAND_SEPARATOR = " ";

    private final CommandLineInterpreter cli; 

    private final InputStream input;

    private final PrintStream output;

    private boolean isRunning = true;



    public CommandLineInterface(CommandLineInterpreter<?> cli, InputStream input, PrintStream output) {

        if (cli == null || hasPredefinedCommands(cli.getCommands())) {

            throw new RuntimeException("CommandLineInterpreter interface of " + cli + " is not properly implemented");

        }

        this.cli = cli;

        this.input = input;

        this.output = output;

    }



    private boolean hasPredefinedCommands(Set<? extends Command<?>> commands) {

        return !Collections.disjoint(commands, getCommands());

    }



    public void start() {

        Scanner scanner = new Scanner(input);

        showHelp();

        while (isRunning) {

            output.print("$>");

            String command = scanner.nextLine();

            List<String> line = Arrays.asList(command.split(COMMAND_SEPARATOR));

            String identifier = line.get(0);

            List<String> parameters = line.subList(1, line.size());

            if (isExecutableCommand(identifier)) {

                Response response = executeCommand(identifier, parameters);

                if (response.failed()) {

                    showResponse(response);

                }

            } else {

                showHelp();

            }

        }

    }



    private boolean isExecutableCommand(String identifier) {

        for (Command cmd : getAllCommands()) {

            if (cmd.isIdentifier(identifier)) {

                return true;

            }

        }

        return false;

    }



    private void showHelp() {

        Set<Command<?>> commands = getAllCommands();

        output.println("help - these commands are available:");

        commands.forEach(c -> output.printf(" - %sn", c.getIdentifier()));

    }



    private void showResponse(Response response) {

        output.println(response);

    }



    @Override

    public Set<Command<CommandLineInterface>> getCommands() {

        Set<Command<CommandLineInterface>> cliCommands = new HashSet<>();

        cliCommands.add(new Command<CommandLineInterface>("exit") {

            @Override

            public Response execute(CommandLineInterface commandLineInterface, List<String> parameter) {

                isRunning = false;

                return Response.success();

            }

        });

        cliCommands.add(new Command<CommandLineInterface>("help") {

            @Override

            public Response execute(CommandLineInterface commandLineInterface, List<String> parameter) {

                showHelp();

                return Response.success();

            }

        });

        return cliCommands;

    }



    private Set<Command<?>> getAllCommands() {

        Set<Command<?>> commands = mapCommands(cli.getCommands());

        commands.addAll(getCommands());

        return commands;

    }



    private Set<Command<?>> mapCommands(Set commands) {

        Set<Command<?>> mappedCommands = new HashSet<>();

        for (Object o : commands) mapCommand(o).ifPresent(mappedCommands::add);

        return mappedCommands;

    }



    private Optional<Command<?>> mapCommand(Object o) {

        return (o instanceof Command<?>) ? Optional.of((Command<?>) o) : Optional.empty();

    }



    @Override

    public Response executeCommand(String identifier, List<String> parameter) {

        Optional<Command<CommandLineInterface>> cmd = getCommands().stream().filter(command -> command.isIdentifier(identifier)).findAny();

        if (cmd.isPresent()) {

            return cmd.get().execute(this, parameter);

        } else {

            return cli.executeCommand(identifier, parameter);

        }

    }



}

Example

if you have implementet the interfaces properly you should have easy to use CLI support for your apps:

public static void main(String args) {

    ExampleApplication app = new ExampleApplication();//implements CommandLineInterpreter

    CommandLineInterface commandLineInterface = new CommandLineInterface(app, System.in, System.out);

    commandLineInterface.start();

}

Output

this is an example output from an example app that does not much...

help - these commands are available:

 - exampleCommand

 - help

 - exit

$>help

help - these commands are available:

 - exampleCommand

 - help

 - exit

$>exampleCommand p1 p2 p3

i could do some actual work now if i were not a mere example, parameter [p1, p2, p3]

$>exit



Process finished with exit code 0