Java Command-Line App with own prompt

Question

I'm writing a JAVA-Console-Application. After the user started the jar he should get a Commandline like the Linux shell, where he can enter commands. This is something I never programmed before. Normaly im writing GUI's or I start the jar with some Arguments which are parsed.

Basicly I have 2 Questions:

1. Is there a third-party-libary which helps reading the user-input from the command line parsing the commands and generating the prompt? To parse args passed in the main class I normally use by Apache Commons CLI. Is it use full here, too or is there a better way?

2. Is there a best practice to provide an "infinite input"? All solutions I found are 10 or more years old like:

   BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
   while(true){
       System.out.print("Enter String");
       String s = br.readLine();
   }
   

   Is this still best practice or is there a better way today?

Answer 1

I am using the library jline2, i.e. with this it's as simple as:

    InputStream inStream = new FileInputStream(FileDescriptor.in);
    ConsoleReader reader = new ConsoleReader("App", inStream, System.out, null);

    reader.setPrompt("> ");

    reader.addCompleter(new FileNameCompleter());
    reader.addCompleter(new StringsCompleter(Arrays.asList(new String[] {
            "cmd1",
            "exit",
            "quit",
    })));

    String line;
    PrintWriter out = new PrintWriter(reader.getOutput());

    while ((line = reader.readLine()) != null) {
        if (line.startsWith("cmd1")) {
            String[] cmd = line.split("\\s+");
            if(cmd.length < 2) {
                out.println("Invalid command");
                help(out);
            } else {
                ... do work
            }
        } else if (line.equalsIgnoreCase("quit") || line.equalsIgnoreCase("exit")) {
            break;
        } else {
            help(out);
        }
    }

    // ensure that all content is written to the screen at the end to make unit tests stable
    reader.flush();