ExcludeAPIFromNMSJar.java

import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.Objects;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.zip.ZipEntry;
import java.util.zip.ZipFile;
import java.util.zip.ZipOutputStream;

public class ExcludeAPIFromNMSJar {
    public static void main(String[] args) throws Exception {
        if (args.length != 1) return;

        File cache = new File(args[0]);
        //noinspection ConstantConditions
        File patchedFile = cache.listFiles((dir, name) -> name.startsWith("patched_") && name.endsWith(".jar"))[0];
        //noinspection ConstantConditions
        File apiFile = cache.listFiles((dir, name) -> name.startsWith("paper-api-") && name.endsWith(".jar"))[0];
        File nmsFile = new File(cache, "nms.jar");

        System.out.println("Excluding " + apiFile.getName() + " files from " + patchedFile.getName() + "..");

        int apiEntriesCount = 0, patchedEntriesCount = 0;
        try (ZipFile patchedZip = new ZipFile(patchedFile);
             ZipFile apiZip = new ZipFile(apiFile);
             ZipOutputStream zos = new ZipOutputStream(new FileOutputStream(nmsFile))) {
            Set<String> apiEntries = apiZip.stream().map(ZipEntry::getName).collect(Collectors.toSet());
            apiEntriesCount = apiEntries.size();
            Iterator<? extends ZipEntry> iterator = patchedZip.entries().asIterator();

            while (iterator.hasNext()) {
                ZipEntry zipEntry = iterator.next();
                patchedEntriesCount++;
                if (apiEntries.contains(zipEntry.getName()))
                    continue;

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

                is.close();
            }
        }

        System.out.println("Excluded " + (patchedEntriesCount - apiEntriesCount)  + " files from final nms jar.");
    }
}