Question

String url = "mysite.com/index.php?name=john&id=432"

How can I extract the id parameter (432)?

it can be in any position in the url and the length of the id varies too

Answer 1

You can use Apache URLEncodedUtils from HttpClient package:

import org.apache.http.NameValuePair;
import org.apache.http.client.utils.URLEncodedUtils;
import java.nio.charset.Charset;
import java.util.List;

public class UrlParsing {
    public static void main(String[] a){
        String url="http://mysite.com/index.php?name=john&id=42";
        List<NameValuePair> args= URLEncodedUtils.parse(url, Charset.defaultCharset());
        for (NameValuePair arg:args)
            if (arg.getName().equals("id"))
                System.out.println(arg.getValue());
    }
}

This print 42 to the console.

If you have the url stored in a URI object, you may find useful an overload of URLEncodedUtils.parse
that accept directly an URI instance. If you use this overloaded version, you have to give the charset as a string:

URI uri = URI.create("http://mysite.com/index.php?name=john&id=42");
List<NameValuePair> args= URLEncodedUtils.parse(uri, "UTF-8");