MD5ハッシュ突き合わせ（Java版） - Clojure版と同じように修正し、Core i5/2.4GHzで550ms程度までパフォーマンスアップ。

gistfile1.java

package example.mdsample.java;

import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import javax.xml.bind.DatatypeConverter;
import org.apache.commons.lang.StringUtils;

public class App {

    public static void main(String[] args) throws Exception {
        for(int i = 0; i < 10; i++) {
            App app = new App();
            long start = System.currentTimeMillis();
            System.out.println("result = " + app.findPassword("hoge", "4b364677946ccf79f841114e73ccaf4f"));
            long end = System.currentTimeMillis();
            System.out.println("Ellapsed Time: " + (end - start) + "ms");
        }
    }

    private final MessageDigest digester;
    
    public App() throws NoSuchAlgorithmException {
        super();
        this.digester = MessageDigest.getInstance("MD5");
    }
        
    private String hexDigest(String s) throws NoSuchAlgorithmException, UnsupportedEncodingException {
        digester.reset();
        digester.update(s.getBytes("UTF-8"));
        byte[] digest = digester.digest();
        return DatatypeConverter.printHexBinary(digest);
    }

    public static class Result {

        public String password;
        public String hash;

        public Result(String password, String hash) {
            this.password = password;
            this.hash = hash;
        }

        @Override
        public String toString() {
            return "Result{" + "password=" + password + ", hash=" + hash + '}';
        }
    }

    private Result findPassword(String salt, String pw) throws NoSuchAlgorithmException, UnsupportedEncodingException {
        for (int i = 0; i < 1000000; i++) {
            String format = StringUtils.leftPad(String.valueOf(i), 6, '0');
            String hex = hexDigest(salt + "$" + format);
            if (pw.toUpperCase().equals(hex)) {
                return new Result(format, hex);
            }
        }
        return null;
    }
}