Bukkit

    public static boolean downloadPlugin(Plugin plugin, String id) {
        InputStreamReader in = null;
        try {
            URL url = new URL("https://api.curseforge.com/servermods/files?projectIds=" + id);
            URLConnection urlConnection = url.openConnection();
            in = new InputStreamReader(urlConnection.getInputStream());
            int numCharsRead;
            char[] charArray = new char[1024];
            StringBuilder sb = new StringBuilder();
            while ((numCharsRead = in.read(charArray)) > 0) {
                sb.append(charArray, 0, numCharsRead);
            }
            String result = sb.toString();
            result = result.replace("\\/", "/").replaceAll(".*\"downloadUrl\":\"", "").split("\",\"")[0];
            String[] split = result.split("/");
            url = new URL(result);
            final String path = plugin.getDataFolder().getParentFile().getAbsoluteFile() + "/" + split[split.length];
            ReadableByteChannel rbc = Channels.newChannel(url.openStream());
            FileOutputStream fos = new FileOutputStream(path);
            fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
            Bukkit.getServer().getLogger().log(Level.INFO, "Finished downloading " + split[split.length] + ". Loading dependecy");
            Bukkit.getServer().getPluginManager().loadPlugin(new File(path));
            return true;
        } catch (MalformedURLException ex) {
            Logger.getLogger(PluginDownloader.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            Logger.getLogger(PluginDownloader.class.getName()).log(Level.SEVERE, null, ex);
        } catch (InvalidPluginException ex) {
            Logger.getLogger(PluginDownloader.class.getName()).log(Level.SEVERE, null, ex);
        } catch (InvalidDescriptionException ex) {
            Logger.getLogger(PluginDownloader.class.getName()).log(Level.SEVERE, null, ex);
        } catch (UnknownDependencyException ex) {
            Logger.getLogger(PluginDownloader.class.getName()).log(Level.SEVERE, null, ex);
        } finally {
            try {
                in.close();
            } catch (IOException ex) {
                Logger.getLogger(PluginDownloader.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
        return false;
    }

this.getServer().getPluginManager().loadPlugin(new File(path));

        if (!this.getServer().getPluginManager().isPluginEnabled("SQLibrary")) {
            try {
                info("Downloadind dependecy: SQLibrary");
                URL url = new URL("http://repo.dakanilabs.com/content/repositories/public/lib/PatPeter/SQLibrary/SQLibrary/maven-metadata.xml");
                URLConnection urlConnection = url.openConnection();
                InputStream in = new BufferedInputStream(urlConnection.getInputStream());

                DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
                DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
                Document doc = dBuilder.parse(in);
                final String version = doc.getElementsByTagName("latest").item(0).getTextContent();
                in.close();
                url = new URL("http://repo.dakanilabs.com/content/repositories/public/lib/PatPeter/SQLibrary/SQLibrary/" + version + "/SQLibrary-" + version + ".jar");
                final String path = plugin.getDataFolder().getParentFile().getAbsoluteFile() + "/SQLibrary-" + version + ".jar";
                ReadableByteChannel rbc = Channels.newChannel(url.openStream());
                FileOutputStream fos = new FileOutputStream(path);
                fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
                info("Finished downloading SQLibrary-" + version + ". Loading dependecy");
                this.getServer().getPluginManager().loadPlugin(new File(path));
                info("Loaded SQLibrary");
            } catch (MalformedURLException ex) {
                error("Failed to download dependency", ex);
            } catch (IOException ex) {
                error("Failed to download dependency", ex);
            } catch (ParserConfigurationException ex) {
                error("Failed to download dependency", ex);
            } catch (SAXException ex) {
                error("Failed to download dependency", ex);
            } catch (InvalidPluginException ex) {
                error("Failed to load dependency", ex);
            } catch (InvalidDescriptionException ex) {
                error("Failed to load dependency", ex);
            } catch (UnknownDependencyException ex) {
                error("Failed to load dependency", ex);
            }
        }