Test.java

public class Test {
  public static void main(String[] argv) {
    MessageDigest md = MessageDigest.getInstance("MD5");
    md.update("test");
    // md5("test")
    System.out.pringln(toHexString(md.digest()));
    
    // md5(md5("test"))
    System.out.pringln(toHexString(md.digest()));
    
  }
  
  private static String toHexString(byte[] in) {
    StringBuilder hexString = new StringBuilder();
    for (int i = 0; i < in.length; i++) {
      String hex = Integer.toHexString(0xFF & in[i]);
      if (hex.length() == 1) {
          hexString.append('0');
      }
      hexString.append(hex);
    }
    return hexString.toString();
  }
}