SetupPaperMC

import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.URL;
import java.nio.channels.Channels;
import java.nio.channels.ReadableByteChannel;
import java.nio.file.Files;
import java.util.Enumeration;
import java.util.zip.ZipEntry;
import java.util.zip.ZipFile;
import java.util.zip.ZipOutputStream;

public class SetupPaperMC {
    public static void main(String[] args) {
        try {
            System.out.println("Setting up PaperMC versions...");
            File cache = new File("cache");
            if (cache.exists()) {
                File[] files = cache.listFiles();
                if (files != null)
                    for (File file : files)
                        file.delete();
            }

            for (int i = 0; i < args.length; i++) {
                String[] v = args[i].split(":");
                File paperclip = new File("paper.jar");

                paperclip.delete();

                System.out.println("Downloading PaperMC " + args[i] + "...");

                ReadableByteChannel rbc = Channels.newChannel(new URL("https://papermc.io/api/v2/projects/paper/versions/" + v[0] + "/builds/" + v[1] + "/downloads/paper-" + v[0] + "-" + v[1] + ".jar").openStream());
                FileOutputStream fos = new FileOutputStream(paperclip);
                fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
                fos.close();
                rbc.close();

                new ProcessBuilder("java", "-Dpaperclip.patchonly=true", "-jar", paperclip.getAbsolutePath())
                        .inheritIO()
                        .start()
                        .waitFor();

                System.out.println("Generating NMS...");

                File[] jars = cache.listFiles();
                if (jars != null)
                    for (File jarFile : jars) {
                        if (jarFile.getName().startsWith("patched_")) {
                            File nmsFile = new File(jarFile.getParentFile(), jarFile.getName().replace("patched_", "nms_"));
                            if (!nmsFile.exists()) {
                                if (i == args.length - 1) {
                                    Files.copy(jarFile.toPath(), nmsFile.toPath());
                                } else {
                                    ZipFile jarZip = new ZipFile(jarFile);

                                    try (ZipOutputStream zos = new ZipOutputStream(new FileOutputStream(nmsFile))) {
                                        Enumeration<? extends ZipEntry> entries = jarZip.entries();
                                        while (entries.hasMoreElements()) {
                                            ZipEntry entry = entries.nextElement();

                                            if (!entry.getName().startsWith("net/minecraft/server/v") && !entry.getName().startsWith("org/bukkit/craftbukkit/v"))
                                                continue;

                                            zos.putNextEntry(entry);
                                            InputStream is = jarZip.getInputStream(entry);
                                            byte[] buf = new byte[1024];
                                            int len;
                                            while((len = is.read(buf)) > 0)
                                                zos.write(buf, 0, len);

                                            is.close();
                                        }
                                    }
                                    jarZip.close();
                                }
                                break;
                            }
                        }
                    }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}