运行Web Scrap程序时出现“线程“主”中的异常java.lang.NullPointerException”错误

我对Web抓取还很陌生，并且对Java的了解有限。

每次我运行此代码，都会收到错误消息：

Exception in thread "main" java.lang.NullPointerException

    at sws.SWS.scrapeTopic(SWS.java:38)
    at sws.SWS.main(SWS.java:26)
Java Result: 1
BUILD SUCCESSFUL (total time: 0 seconds)

我的代码是：

import java.io.*;

import java.net.*;

import org.jsoup.Jsoup;

import org.jsoup.nodes.Document;

public class SWS
{

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args)
    {
        scrapeTopic("wiki/Python");

    }

    public static void scrapeTopic(String url)
    {
        String html = getUrl("http://www.wikipedia.org/" + url);



        Document doc = Jsoup.parse(html);

        String contentText = doc.select("#mw-content-text > p").first().text();

        System.out.println(contentText);


    }


    public static String getUrl(String Url)
    {
        URL urlObj = null;

        try 
        {
            urlObj = new URL(Url);

        }

        catch(MalformedURLException e)
        {
            System.out.println("The url was malformed");

            return "";
        }


        URLConnection urlCon = null;

        BufferedReader in = null;

        String outputText = "";

        try
        {
            urlCon = urlObj.openConnection();

            in = new BufferedReader(new InputStreamReader(urlCon.getInputStream()));
             String line = "";

             while ((line = in.readLine()) != null)
             {
                 outputText += line;

             }

             in.close();
        }

         catch(IOException e)
         {
             System.out.println("There was a problem connecting to the url");

             return "";

         }

        return outputText;



    }

}

我一直盯着屏幕看已有一段时间，需要帮助！

提前致谢。