Bukkit

// Declares the Package and all Imports

package de.craiz.uptime;

import java.io.File;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;

import org.bukkit.ChatColor;
import org.bukkit.command.Command;
import org.bukkit.command.CommandExecutor;
import org.bukkit.command.CommandSender;
import org.bukkit.configuration.file.FileConfiguration;
import org.bukkit.configuration.file.YamlConfiguration;
import org.bukkit.plugin.java.JavaPlugin;

// Declares JavaPlugin as Super Class and makes this class a Command Executor

public class UpTime extends JavaPlugin implements CommandExecutor {

   // Command Method:

    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {

        // Checks if the command is uptime.

        // If not: Do Nothing
        if(cmd.getName().equalsIgnoreCase("uptime")) {

            // Checks if the Sender (Console or Player) has Permission to execute this command
            if(sender.hasPermission("xuptime.see") | sender.hasPermission("xuptime.started")) {

                // Checks if the commands has any arguments
                if(args.length == 0) {

                    // Checks if the Sender has Permission to see the UpTime
                   if(sender.hasPermission("xuptime.see")) {

                        // Calculates for how long (in millis) the server has been running by simply doing

                        // Time Now (in millis) (since 1970) - Time when the Server started (in millis) (since 1970)
                        long on = System.currentTimeMillis() - stat;

                        // Creates a new SimpleDateFormat Instance with the Pattern:

                        // Hours : Minutes : Second

                        // e.g.: 11:35:23
                        SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");

                        // Sets the TimeZone
                        sdf.setTimeZone(TimeZone.getTimeZone(timezone));

                        // Formats for the long defined above and splits it with : as regex
                        String[] df = sdf.format(new Date(on)).split(":");

                        // This String is representing the Hour:
                        String h = df[0];

                        // This String is representing the Minute:
                        String m = df[1];

                        // This String is representing the Second:
                        String s = df[2];

                        // Formats a String, replaces all valid placeholders and sends it to the Sender
                        String msg = uptime.replace("{h}", h).replace("{m}", m).replace("{s}", s);
                        sender.sendMessage(ChatColor.translateAlternateColorCodes('&', msg));
                   } else {

                        // Sets the Default TimeZone (To avoid issues)
                        TimeZone.setDefault(TimeZone.getTimeZone(timezone));

                        // Creates a new SimpleDateFormat Instance with the Pattern:

                        // Day : Month : Year : Hour : Minute : Second : Milli Second

                        // e.g.: 21:12:2016:08:58:25:285
                        SimpleDateFormat sdf = new SimpleDateFormat("dd:MM:yyyy:HH:mm:ss:SSS");

                        // Sets the TimeZone (Again to avoid issues)
                        sdf.setTimeZone(TimeZone.getTimeZone(timezone));

                        // Formats for time (in millis) (since 1970) when the server started and splits it with : as regex
                        String[] df = sdf.format(new Date(stat)).split(":");

                        // This String is representing the Day:
                        String d = df[0];

                        // This String is representing the Month:
                        String m = df[1];

                        // This String is representing the Year:
                        String y = df[2];

                        // This String is representing the Hour:
                        String h = df[3];

                        // This String is representing the Minute:
                        String min = df[4];

                        // This String is representing the Second:
                        String sec = df[5];

                        // This String is representing the Milli Second
                        String ms = df[6];

                        // This String is representing the TimeZone
                        String timezone = this.timezoner;

                        // Formats a String, replaces all valid placeholders and sends it to the sender
                        String msg = this.started.replace("{d}", d).replace("{m}", m).replace("{y}", y).replace("{h}", h).replace("{min}", min).replace("{sec}", sec).replace("{ms}", ms).replace("{timezone}", timezone);
                        sender.sendMessage(ChatColor.translateAlternateColorCodes('&', msg));
                    }

                // Checks if the Command has any arguments
                } else if(args.length == 1) {

                    // Checks if the Commands Argument is started
                    if(args[0].equalsIgnoreCase("started")) {

                        // Checks if the Sender has Permission for this Command
                        if(sender.hasPermission("xuptime.started")) {

                            // See above:
                            TimeZone.setDefault(TimeZone.getTimeZone(timezone));
                            SimpleDateFormat sdf = new SimpleDateFormat("dd:MM:yyyy:HH:mm:ss:SSS");
                            sdf.setTimeZone(TimeZone.getTimeZone(timezone));
                            String[] df = sdf.format(new Date(stat)).split(":");
                            String d = df[0];
                            String m = df[1];
                            String y = df[2];
                            String h = df[3];
                            String min = df[4];
                            String sec = df[5];
                            String ms = df[6];
                            String timezone = this.timezoner;
                            String msg = this.started.replace("{d}", d).replace("{m}", m).replace("{y}", y).replace("{h}", h).replace("{min}", min).replace("{sec}", sec).replace("{ms}", ms).replace("{timezone}", timezone);
                            sender.sendMessage(ChatColor.translateAlternateColorCodes('&', msg));
                        } else {

                            // See above:
                            long on = System.currentTimeMillis() - stat;
                            SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");
                            sdf.setTimeZone(TimeZone.getTimeZone(timezone));
                            String[] df = sdf.format(new Date(on)).split(":");
                            String h = df[0];
                            String m = df[1];
                            String s = df[2];
                            String msg = uptime.replace("{h}", h).replace("{m}", m).replace("{s}", s);
                            sender.sendMessage(ChatColor.translateAlternateColorCodes('&', msg));
                        }
                    }
                } else {

                    // This happens if the Command was not executed correctly
                    sender.sendMessage(ChatColor.translateAlternateColorCodes('&', usage));
                }
            } else {

                // This happens if the Sender had not enough Permissions
                sender.sendMessage(ChatColor.translateAlternateColorCodes('&', noperm));
            }
        }

        // Returns true so no Usage Message is printed by Bukkit
        return true;
    }

    // This happens on Startup:
    public void onEnable() {

        // Loads the Config:
        loadConfig();

        // Saves the Config Values into Variables:
        readConfig();

        // Sets this Class as the Executor of UpTime
        this.getCommand("uptime").setExecutor(this);

        // Declares the StartUp Time (in millis) (since 1970)
        stat = System.currentTimeMillis();

        // Sets the Default TimeZone (To avoid issues)
        TimeZone.setDefault(TimeZone.getTimeZone(timezone));
    }

    // This Long is representing the StartUp Time (in millis) (since 1970)
    private long stat = 0L;

    // This String is representing the Help Url

    // Useless since it's literally final and used by only 1 method
    private String helpurl = "http://forum.decraiz.bplaced.net";

    // Placeholder for a Config Value but has it's default Value in case of an error when overwriting from Config
    private String uptime = "&9This server is running for &e{h} &9hours &e{m} &9minutes and &e{s} &9seconds.";

    // Placeholder for a Config Value but has it's default Value in case of an error when overwriting from Config
    private String started = "&9This server is running since &e{d}/{m}/{y} &9at &e{h}:{min}:{sec}.{ms} &9in the &e{timezone} &9TimeZone";

    // Placeholder for a Config Value but has it's default Value in case of an error when overwriting from Config
    private String timezone = "GMT";

    // Placeholder for a Config Value but has it's default Value in case of an error when overwriting from Config
    private String timezoner = "GMT";

    // Placeholder for a Config Value but has it's default Value in case of an error when overwriting from Config
    private String usage = "&cUsage: /uptime (started)";

    // Placeholder for a Config Value but has it's default Value in case of an error when overwriting from Config
    private String noperm = "&cSorry, but you don't have permission to perform this action.";

    private File getCfgF() {

        // Returns the Config File

        // Creation is done by YamlConfiguration
        return new File("plugins/xUpTime", "config.yml");
    }

    private FileConfiguration getCfg() {

        // Returns the Config Configuration and creates the file (if not done yet)
        return YamlConfiguration.loadConfiguration(getCfgF());
    }

    private boolean loadConfig() {
        FileConfiguration cfg = getCfg();

        // Allows to create Values / Header
        cfg.options().copyDefaults(true);
        cfg.options().copyHeader(true);

        // Sets Header:
        cfg.options().header("Visit "+helpurl+" for help");

        // Sets Default Values:
        cfg.addDefault("Settings.TimeZone.Java", "GMT");
        cfg.addDefault("Settings.TimeZone.Display", "GMT");
        cfg.addDefault("Message.UpTime", "&9This server is running for &e{h} &9hours &e{m} &9minutes and &e{s} &9seconds.");
        cfg.addDefault("Message.Started", "&9This server is running since &e{d}/{m}/{y} &9at &e{h}:{min}:{sec}.{ms} &9in the &e{timezone} &9TimeZone");
        cfg.addDefault("Error.Usage", "&cUsage: {usage}");
        cfg.addDefault("Error.NoPermission", "&cSorry, but you don't have permission to perform this action.");
        try {

            // Saves the File
            cfg.save(getCfgF());
        } catch (IOException e) {

            // Prints (in case of an error) a detailed report about it
            e.printStackTrace();

            // Returns False because of Error
            return false;
        }

        // Returns True because of no Error
        return true;
    }

    private void readConfig() {
        FileConfiguration cfg = getCfg();

        // Overwrites all Variables with their Config Values
        this.timezone = cfg.getString("Settings.TimeZone.Java");
        this.timezoner = cfg.getString("Settings.TimeZone.Display");
        this.uptime = cfg.getString("Message.UpTime");
        this.started = cfg.getString("Message.Started");
        this.usage = cfg.getString("Error.Usage");
        this.noperm = cfg.getString("Error.NoPermission");
    }

}