Read-eval-print loop in CraftBukkit.

REPLBukkit.java

package com.comphenix.example;
import java.util.concurrent.TimeUnit;
import javax.script.*;
import org.apache.commons.lang.StringUtils;
import org.apache.commons.lang.exception.ExceptionUtils;
import org.bukkit.ChatColor;
import org.bukkit.command.*;
import org.bukkit.conversations.*;
import org.bukkit.event.Listener;
import org.bukkit.plugin.java.JavaPlugin;
import com.google.common.util.concurrent.Uninterruptibles;
public class REPLBukkit extends JavaPlugin implements Listener {
    final ScriptEngine engine = new ScriptEngineManager().getEngineByName("js");
    public synchronized boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
        if (command.getName().equals("js") && sender instanceof Conversable) {
            ((Conversable) sender).beginConversation(new Conversation(this, (Conversable) sender, new StringPrompt() {
                private String lastLine = "", lines = "";
                private volatile int state;
                private int lineCount = 0;
                public String getPromptText(ConversationContext context) { return lastLine; }
                public Prompt acceptInput(final ConversationContext context, String line) {                  
                    lines += (lastLine = line) + "\n";
                    lineCount++;
                    Thread t = new Thread(new Runnable() {
                        public void run() {
                            try {
                                state = 0; // State.INTERRUPTED
                                context.getForWhom().sendRawMessage("> " + engine.eval(lines));
                                state = 1; // State.DONE
                            } catch (Exception e) {
                                if (!(e instanceof ScriptException) || ((ScriptException) e).getLineNumber() != lineCount) {
                                    for (String errorLine : ExceptionUtils.getMessage(e).split("/n"))
                                        context.getForWhom().sendRawMessage(ChatColor.RED + errorLine);
                                    state = 1; // State.DONE
                                } else 
                                    state = 2; // State.MORE_LINES
                            }
                        }
                    });
                    t.start();
                    Uninterruptibles.joinUninterruptibly(t, 5, TimeUnit.SECONDS);
                    if (state == 0) t.stop();
                    return state == 2 ? this : Prompt.END_OF_CONVERSATION;
                }
            }) {{ localEchoEnabled = false; }});
            ((Conversable) sender).acceptConversationInput(StringUtils.join(args, " "));
        }
        return true;
    }
}