You need some html parser like it is Jsoup. Its easy simple and effective library. Down there you can see one my random implementation, I did for answering another question similar to this one. .getElementById(id); is the method you are looking for...

import org.apache.http.protocol.HTTP;
import org.jsoup.*;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements;

public class start extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
       try {
        Document doc = Jsoup.connect(URL).get();
        Log.i("DOC", doc.toString().toString());
    Elements elementsHtml = doc.getElementById(id);
        for(Element element: elementsHtml)
        {
            Log.i("ELEMENTI",URLDecoder.decode(element.text(), HTTP.UTF_8));
        }

    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

Here you can get the Jsoup

For writing the file use FileWriter or any other class that allows you to write to file

Do not forget to add permision for connecting to internet in your Manifest