Absolute minimum code to get a valid oauth_signature populated in Java or Groovy?

Here is my code for Flickr OAuth. NOTICE: I REFERED some logic from SignPost. It is really very tricky to generate it signature…. OK. This is just an example for generate the “oauth_signature”

package oauthflickr;

import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.net.URI;
import java.net.URISyntaxException;
import java.net.URLEncoder;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.List;

import javax.crypto.Mac;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

import org.apache.commons.codec.binary.Base64;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.utils.URIUtils;
import org.apache.http.client.utils.URLEncodedUtils;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;

/**
 * a simple program to get flickr token and token secret.
 * 
 * @author Mark Zang
 * 
 */
public class OAuthForFlickr {

    private static String key = "_________________________";
    private static String secret = "___________";

    private static final String HMAC_SHA1 = "HmacSHA1";

    private static final String ENC = "UTF-8";

    private static Base64 base64 = new Base64();

    /**
     * 
     * @param url
     *            the url for "request_token" URLEncoded.
     * @param params
     *            parameters string, URLEncoded.
     * @return
     * @throws UnsupportedEncodingException
     * @throws NoSuchAlgorithmException
     * @throws InvalidKeyException
     */
    private static String getSignature(String url, String params)
            throws UnsupportedEncodingException, NoSuchAlgorithmException,
            InvalidKeyException {
        /**
         * base has three parts, they are connected by "&": 1) protocol 2) URL
         * (need to be URLEncoded) 3) Parameter List (need to be URLEncoded).
         */
        StringBuilder base = new StringBuilder();
        base.append("GET&");
        base.append(url);
        base.append("&");
        base.append(params);
        System.out.println("Stirng for oauth_signature generation:" + base);
        // yea, don't ask me why, it is needed to append a "&" to the end of
        // secret key.
        byte[] keyBytes = (secret + "&").getBytes(ENC);

        SecretKey key = new SecretKeySpec(keyBytes, HMAC_SHA1);

        Mac mac = Mac.getInstance(HMAC_SHA1);
        mac.init(key);

        // encode it, base64 it, change it to string and return.
        return new String(base64.encode(mac.doFinal(base.toString().getBytes(
                ENC))), ENC).trim();
    }

    /**
     * @param args
     * @throws IOException
     * @throws ClientProtocolException
     * @throws URISyntaxException
     * @throws NoSuchAlgorithmException
     * @throws InvalidKeyException
     */
    public static void main(String[] args) throws ClientProtocolException,
            IOException, URISyntaxException, InvalidKeyException,
            NoSuchAlgorithmException {

        HttpClient httpclient = new DefaultHttpClient();
        List<NameValuePair> qparams = new ArrayList<NameValuePair>();
        // These params should ordered in key
        qparams.add(new BasicNameValuePair("oauth_callback", "oob"));
        qparams.add(new BasicNameValuePair("oauth_consumer_key", key));
        qparams.add(new BasicNameValuePair("oauth_nonce", ""
                + (int) (Math.random() * 100000000)));
        qparams.add(new BasicNameValuePair("oauth_signature_method",
                "HMAC-SHA1"));
        qparams.add(new BasicNameValuePair("oauth_timestamp", ""
                + (System.currentTimeMillis() / 1000)));
        qparams.add(new BasicNameValuePair("oauth_version", "1.0"));

        // generate the oauth_signature
        String signature = getSignature(URLEncoder.encode(
                "http://www.flickr.com/services/oauth/request_token", ENC),
                URLEncoder.encode(URLEncodedUtils.format(qparams, ENC), ENC));

        // add it to params list
        qparams.add(new BasicNameValuePair("oauth_signature", signature));

        // generate URI which lead to access_token and token_secret.
        URI uri = URIUtils.createURI("http", "www.flickr.com", -1,
                "/services/oauth/request_token",
                URLEncodedUtils.format(qparams, ENC), null);

        System.out.println("Get Token and Token Secrect from:"
                + uri.toString());

        HttpGet httpget = new HttpGet(uri);
        // output the response content.
        System.out.println("oken and Token Secrect:");

        HttpResponse response = httpclient.execute(httpget);
        HttpEntity entity = response.getEntity();
        if (entity != null) {
            InputStream instream = entity.getContent();
            int len;
            byte[] tmp = new byte[2048];
            while ((len = instream.read(tmp)) != -1) {
                System.out.println(new String(tmp, 0, len, ENC));
            }
        }
    }

}