InputStreamReader(urlConn.getInputStream())报NullPointerException

InputStreamReader(urlConn.getInputStream())报NullPointerException

在学习Mars Android教程“[Android开发视频教学].01_18_文件下载”时遇到个问题，请指教
class DownFileClickListener implements OnClickListener{ 
        @Override 
        public void onClick(View v) { 
            String urlStr="http://127.0.0.1/1.txt"; 
            try { 
                /*
                 * 通过URL取得HttpURLConnection
                 * 要网络连接成功，需在AndroidMainfest.xml中进行权接待方案 限配置
                 * <uses-permission android:name="android.permission.INTERNET" />
                 */ 
                URL url=new URL(urlStr); 
                HttpURLConnection conn=(HttpURLConnection)url.openConnection(); 
                //取得inputStream，并进行读取 
                InputStream input=conn.getInputStream(); 
                BufferedReader in=new BufferedReader(new InputStreamReader(input)); 
                String line=null; 
                StringBuffer sb=new StringBuffer(); 
                while((line=in.readLine())!=null){ 
                    sb.append(line); 
                } 
                System.out.println(sb.toString()); 
                 
            } catch (MalformedURLException e) { 
                e.printStackTrace(); 
            } catch (IOException e) { 
                e.printStackTrace(); 
            } 
        } 
    } 

 InputStream input=conn.getInputStream(); 
执行到这一句的时候会报错：
java.lang.NullPointerException

不知道是不是自己的URL地址有问题
模拟器吗，模拟器的话地址ip改成http://10.0.2.2/1.txt