gistfile1.java

/* Outputs gem filenames from spec files.
 * Full set of public gems:
 *   https://rubygems.org/specs.4.8
 * + https://rubygems.org/prerelease_specs.4.8
 */

import org.jruby.Ruby;
import org.jruby.RubyArray;
import org.jruby.RubyObject;
import org.jruby.runtime.marshal.UnmarshalStream;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class gemlist {
    public static void main(String[] args) throws IOException {
        final long l1 = System.currentTimeMillis();

        final File file = new File(args[0]);
        final FileInputStream fileInputStream = new FileInputStream(file);

        final Ruby ruby = Ruby.newInstance();
        ruby.evalScriptlet("module Gem; class Version; def marshal_load array; @version = array[0]; end; end; end");

        final UnmarshalStream stream = new UnmarshalStream(ruby, fileInputStream, null, false);
        final RubyArray array = stream.unmarshalObject().convertToArray();
        final List<String> filenames = new ArrayList<String>();
        for (Object o : array) {
            RubyArray arr = ((RubyObject) o).convertToArray();
            final String name = arr.get(0).toString();
            final String version = ((RubyObject) arr.get(1)).getInstanceVariable("@version").toString();
            final String platform = arr.get(2).toString();

            final StringBuilder builder = new StringBuilder(name);
            builder.append('-');
            builder.append(version);
            if (!"ruby".equals(platform)) {
                builder.append('-');
                builder.append(platform);
            }
            builder.append(".gem");
            filenames.add(builder.toString());
        }

        final long l2 = System.currentTimeMillis();

        for (String filename : filenames) {
            System.out.println(filename);
        }

        System.err.println(filenames.size());
        System.err.println((l2 - l1) + "ms");
    }
}