Picocli Shell JLine2 contains components and documentation for building interactive shell command line applications with JLine 2 and picocli.
JLine and picocli complement each other very well and have little or none functional overlap.
JLine provides interactive shell functionality but has no built-in command line parsing functionality. What it does provide is a tokenizer for splitting a single command line String into an array of command line argument Strings.
Given an array of Strings, picocli can execute a command or subcommand. Combining these two libraries makes it easy to build powerful interactive shell applications.
JLine 2 is a well-known library for building interactive shell applications. From the JLine web site:
JLine is a Java library for handling console input. It is similar in functionality to BSD editline and GNU readline but with additional features that bring it in par with ZSH line editor.
Picocli is a Java command line parser with both an annotations API and a programmatic API, featuring usage help with ANSI colors, autocomplete and nested subcommands.
The picocli user manual is here, and the GitHub project is here.
PicocliJLineCompleter is a small component that generates completion candidates to allow users to
get command line TAB auto-completion for a picocli-based application running in a JLine 2 shell.
import java.io.IOException;
import java.io.PrintWriter;
import java.util.concurrent.Callable;
import java.util.concurrent.TimeUnit;
import jline.console.ConsoleReader;
import jline.console.completer.ArgumentCompleter.ArgumentList;
import jline.console.completer.ArgumentCompleter.WhitespaceArgumentDelimiter;
import picocli.CommandLine;
import picocli.CommandLine.Command;
import picocli.CommandLine.IFactory;
import picocli.CommandLine.Model.CommandSpec;
import picocli.CommandLine.Option;
import picocli.CommandLine.ParentCommand;
import picocli.CommandLine.Spec;
import picocli.shell.jline2.PicocliJLineCompleter;
/**
* Example that demonstrates how to build an interactive shell with JLine and picocli.
* @since 3.7
*/
public class Example {
/**
* Top-level command that just prints help.
*/
@Command(name = "", description = "Example interactive shell with completion",
footer = {"", "Press Ctl-D to exit."},
subcommands = {MyCommand.class, ClearScreen.class, ReadInteractive.class})
static class CliCommands implements Runnable {
final ConsoleReader reader;
final PrintWriter out;
@Spec
private CommandSpec spec;
CliCommands(ConsoleReader reader) {
this.reader = reader;
out = new PrintWriter(reader.getOutput());
}
public void run() {
out.println(spec.commandLine().getUsageMessage());
}
}
/**
* A command with some options to demonstrate completion.
*/
@Command(name = "cmd", mixinStandardHelpOptions = true, version = "1.0",
description = "Command with some options to demonstrate TAB-completion" +
" (note that enum values also get completed)")
static class MyCommand implements Runnable {
@Option(names = {"-v", "--verbose"})
private boolean[] verbosity = {};
@Option(names = {"-d", "--duration"})
private int amount;
@Option(names = {"-u", "--timeUnit"})
private TimeUnit unit;
@ParentCommand CliCommands parent;
public void run() {
if (verbosity.length > 0) {
parent.out.printf("Hi there. You asked for %d %s.%n", amount, unit);
} else {
parent.out.println("hi!");
}
}
}
/**
* Command that clears the screen.
*/
@Command(name = "cls", aliases = "clear", mixinStandardHelpOptions = true,
description = "Clears the screen", version = "1.0")
static class ClearScreen implements Callable<Void> {
@ParentCommand CliCommands parent;
public Void call() throws IOException {
parent.reader.clearScreen();
return null;
}
}
/**
* Command that optionally reads and password interactively.
*/
@Command(name = "pwd", mixinStandardHelpOptions = true,
description = "Interactivly reads a password", version = "1.0")
static class ReadInteractive implements Callable<Void> {
@Option(names = {"-p"}, parameterConsumer = InteractiveParameterConsumer.class)
private String password;
@ParentCommand CliCommands parent;
public Void call() throws Exception {
if(password == null) {
parent.out.println("No password prompted");
} else {
parent.out.println("Password is '" + password + "'");
}
return null;
}
}
public static void main(String[] args) {
try {
ConsoleReader reader = new ConsoleReader();
IFactory factory = new CustomFactory(new InteractiveParameterConsumer(reader));
// set up the completion
CliCommands commands = new CliCommands(reader);
CommandLine cmd = new CommandLine(commands, factory);
reader.addCompleter(new PicocliJLineCompleter(cmd.getCommandSpec()));
// start the shell and process input until the user quits with Ctl-D
String line;
while ((line = reader.readLine("prompt> ")) != null) {
ArgumentList list = new WhitespaceArgumentDelimiter()
.delimit(line, line.length());
new CommandLine(commands, factory)
.execute(list.getArguments());
}
} catch (Throwable t) {
t.printStackTrace();
}
}
}import java.io.IOException;
import java.util.Stack;
import jline.console.ConsoleReader;
import picocli.CommandLine;
import picocli.CommandLine.IParameterConsumer;
import picocli.CommandLine.Model.ArgSpec;
import picocli.CommandLine.Model.CommandSpec;
import picocli.CommandLine.Option;
import picocli.CommandLine.Parameters;
/**
* <p>A parameter consumer for interactively entering a value (e.g. a password).
* <p>Similar to {@link Option#interactive()} and {@link Parameters#interactive()}.
* Picocli's interactive and JLine's {@link ConsoleReader} do not work well together.
* Thus delegating reading input to {@link ConsoleReader} should be preferred.
* @since 4.0
*/
public class InteractiveParameterConsumer implements IParameterConsumer {
private final ConsoleReader reader;
public InteractiveParameterConsumer(ConsoleReader reader) {
this.reader = reader;
}
public void consumeParameters(Stack<String> args, ArgSpec argSpec, CommandSpec commandSpec) {
try {
argSpec.setValue(reader.readLine(String
.format("Enter %s: ", argSpec.paramLabel()), '\0'));
} catch (IOException e) {
throw new CommandLine.ParameterException(commandSpec.commandLine()
, "Error while reading interactivly", e, argSpec, "");
}
}
}import java.util.Arrays;
import java.util.List;
import picocli.CommandLine;
import picocli.CommandLine.IFactory;
/**
* <p>Can serve for {@link #create(Class)} from a list of given instances or
* delegates to a {@link CommandLine#defaultFactory()} if no objects for class
* available.
* <p>Usually this would be done with
* <a href="https://picocli.info/#_dependency_injection">dependency injection</a>.
* @since 4.0
* @see <a href="https://picocli.info/#_dependency_injection">https://picocli.info/#_dependency_injection</a>
*/
public class CustomFactory implements IFactory {
private final IFactory factory = CommandLine.defaultFactory();
private final List<Object> instances;
public CustomFactory(Object... instances) {
this.instances = Arrays.asList(instances);
}
public <K> K create(Class<K> cls) throws Exception {
for(Object obj : instances) {
if(cls.isAssignableFrom(obj.getClass())) {
return cls.cast(obj);
}
}
return factory.create(cls);
}
}