Jsoup returning no value

I have a problem with Jsoup library, which when I try to make the connection to a certain page, it simply does not return any value from the connection.

public static void main(String[] args) {

    try{

        Document doc = Jsoup.connect("http://pt.stackoverflow.com/").get();

        //Pegando elemento das perguntas
        Elements elements = doc.select("a.question-hyperlink");

        System.out.println("O  titulo da página é: "+doc.title());

        //exibindo titulo da pergunta
        for(int i = 0; i <elements.size(); i++){
            System.out.println(elements.get(i).text());
        }
    }catch(Exception e){
        System.out.println("Erro "+ e);
    }
}

By coincidence I tested it with Stack Overflow and it gave the same problem.

Netbeans IDE Return:

Erro: org.jsoup.HttpStatusException: HTTP error fetching URL. Status=403, URL=http://pt.stackoverflow.com/

------------------------------------------------------------------------
BUILD SUCCESS
------------------------------------------------------------------------
Total time: 1.282s
Finished at: Sun May 15 13:26:41 BRT 2016
Final Memory: 5M/109M
------------------------------------------------------------------------

I do not know if this influences something, but the project type is Maven.

@EDIT

I was able to resolve the problem by adding the following method to the connection.

Document doc = Jsoup.connect("http://pt.stackoverflow.com/")
                .userAgent("Mozilla").get();