Hi, I am trying to get the access token in Java and following the instructions on http://www.salesforce.com/us/developer/docs/chatterapi/index.htm
But I continuously get this error:

{"error":"unsupported_grant_type","error_description":"grant type not supported"}

My codes are here:

package admin;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.simple.JSONObject;
import org.json.simple.JSONValue;

import com.google.gson.Gson;

public class REST
{
String authURL = "https://login.salesforce.com/services/oauth2/authorize";
String tokenURL = "https://na14.salesforce.com/services/oauth2/token";
public static void main(String[] args) throws ClientProtocolException, IOException
{
REST rest = new REST();
}

public REST() throws ClientProtocolException, IOException
{
HttpClient httpclient = new DefaultHttpClient();
HttpPost post = new HttpPost(tokenURL);
post.getParams().setParameter("client_id", "3MVG9rFJvQRVOvk6sl7xMXtrbyQb2XUv2vprLKWv0uxBLKFzNqtHJG6cmzuemPYDB3hPwqXsBlw0BGQPkb81P");
post.getParams().setParameter("client_secret", "4864720658246552438");
post.getParams().setParameter("grant_type", "password");
post.getParams().setParameter("username", "XXXX");
post.getParams().setParameter("password", "XXXX");
post.getParams().setParameter("redirect_uri", "https://login.salesforce.com/services/oauth2/success");
HttpResponse response = httpclient.execute(post);
JSONObject json = (JSONObject) JSONValue.parse(new InputStreamReader (response.getEntity().getContent()));
System.out.println(json);
}
}